normalize timestamps and fix framerate metadata in init file

package/android/src/main/java/com/mrousavy/camera/core/CameraSession.kt

@@ -429,15 +429,15 @@ class CameraSession(private val context: Context, private val cameraManager: Cam
       // Get actual device rotation from WindowManager since the React Native orientation hook
       // doesn't update when rotating between landscape-left and landscape-right on Android.
       // Map device rotation to the correct orientationHint for video recording:
-      // - Counter-clockwise (ROTATION_90) → 90° hint
-      // - Clockwise (ROTATION_270) → 270° hint
+      // - Counter-clockwise (ROTATION_90) → 270° hint
+      // - Clockwise (ROTATION_270) → 90° hint
       val windowManager = context.getSystemService(Context.WINDOW_SERVICE) as WindowManager
       val deviceRotation = windowManager.defaultDisplay.rotation
       val recordingOrientation = when (deviceRotation) {
         Surface.ROTATION_0 -> Orientation.PORTRAIT
-        Surface.ROTATION_90 -> Orientation.LANDSCAPE_LEFT
+        Surface.ROTATION_90 -> Orientation.LANDSCAPE_RIGHT
         Surface.ROTATION_180 -> Orientation.PORTRAIT_UPSIDE_DOWN
-        Surface.ROTATION_270 -> Orientation.LANDSCAPE_RIGHT
+        Surface.ROTATION_270 -> Orientation.LANDSCAPE_LEFT
         else -> Orientation.PORTRAIT
       }
 
@@ -448,7 +448,7 @@ class CameraSession(private val context: Context, private val cameraManager: Cam
         enableAudio,
         fps,
         videoOutput.enableHdr,
-        recordingOrientation,
+        orientation,
         options,
         filePath,
         callback,

package/android/src/main/java/com/mrousavy/camera/core/FragmentedRecordingManager.kt

@@ -20,8 +20,7 @@ import java.io.File
  */
 class FragmentedRecordingManager(
     private val encoder: MediaCodec,
-    private val muxer: HlsMuxer,
-    private val configuredFps: Int
+    private val muxer: HlsMuxer
 ) : MediaCodec.Callback(), ChunkedRecorderInterface {
 
     companion object {
@@ -40,21 +39,19 @@ class FragmentedRecordingManager(
             segmentDurationSeconds: Int = DEFAULT_SEGMENT_DURATION_SECONDS
         ): FragmentedRecordingManager {
             val mimeType = options.videoCodec.toMimeType()
-            // Use cameraOrientation from Android (computed from device rotation)
-            // instead of options.orientation from JS which may be stale
-            val recordingOrientationDegrees = cameraOrientation.toDegrees()
+            val cameraOrientationDegrees = cameraOrientation.toDegrees()
+            val recordingOrientationDegrees = (options.orientation ?: Orientation.PORTRAIT).toDegrees()
 
-            // Swap dimensions based on orientation - same logic as ChunkedRecordingManager
-            // When camera is in landscape orientation, we need to swap width/height for the encoder
+            // Swap dimensions based on camera orientation, same as ChunkedRecordingManager
             val (width, height) = if (cameraOrientation.isLandscape()) {
                 size.height to size.width
             } else {
                 size.width to size.height
             }
 
-            Log.d(TAG, "Input size: ${size.width}x${size.height}, " +
-                    "encoder size: ${width}x${height}, " +
-                    "orientation: $cameraOrientation ($recordingOrientationDegrees°)")
+            Log.d(TAG, "Input size: ${size.width}x${size.height}, encoder size: ${width}x${height}, " +
+                    "cameraOrientation: $cameraOrientation ($cameraOrientationDegrees°), " +
+                    "recordingOrientation: $recordingOrientationDegrees°")
 
             val format = MediaFormat.createVideoFormat(mimeType, width, height)
             val codec = MediaCodec.createEncoderByType(mimeType)
@@ -64,7 +61,12 @@ class FragmentedRecordingManager(
                 MediaCodecInfo.CodecCapabilities.COLOR_FormatSurface
             )
 
-            val effectiveFps = fps ?: 30
+            // Use 30fps as conservative default since many Android devices can't sustain
+            // higher frame rates at high resolutions. This affects:
+            // - Encoder: bitrate allocation and I-frame interval calculation
+            // - HlsMuxer: timescale for accurate sample durations
+            // The actual frame timing comes from camera timestamps regardless of this setting.
+            val effectiveFps = 30
             format.setInteger(MediaFormat.KEY_FRAME_RATE, effectiveFps)
             format.setInteger(MediaFormat.KEY_I_FRAME_INTERVAL, segmentDurationSeconds)
             format.setInteger(MediaFormat.KEY_BIT_RATE, bitRate)
@@ -73,7 +75,7 @@ class FragmentedRecordingManager(
 
             codec.configure(format, null, null, MediaCodec.CONFIGURE_FLAG_ENCODE)
 
-            // Create muxer with callbacks and orientation
+            // Create muxer with callbacks, orientation, and fps
             val muxer = HlsMuxer(
                 outputDirectory = outputDirectory,
                 callback = object : HlsMuxer.Callback {
@@ -85,13 +87,14 @@ class FragmentedRecordingManager(
                         callbacks.onVideoChunkReady(file, index, durationUs)
                     }
                 },
-                orientationDegrees = recordingOrientationDegrees
+                orientationDegrees = recordingOrientationDegrees,
+                fps = effectiveFps
             )
             muxer.setSegmentDuration(segmentDurationSeconds * 1_000_000L)
 
-            Log.d(TAG, "Created HlsMuxer with orientation: $recordingOrientationDegrees degrees, fps: $effectiveFps")
+            Log.d(TAG, "Created HlsMuxer with orientation: $recordingOrientationDegrees degrees")
 
-            return FragmentedRecordingManager(codec, muxer, effectiveFps)
+            return FragmentedRecordingManager(codec, muxer)
         }
     }
 
@@ -171,8 +174,7 @@ class FragmentedRecordingManager(
         synchronized(this) {
             Log.i(TAG, "Output format changed: $format")
 
-            // Pass configured fps to muxer (not the encoder's output format fps which may differ)
-            trackIndex = muxer.addTrack(format, configuredFps)
+            trackIndex = muxer.addTrack(format)
             muxer.start()
             muxerStarted = true
         }

package/android/src/main/java/com/mrousavy/camera/core/HlsMuxer.kt

@@ -27,7 +27,8 @@ import java.nio.ByteBuffer
 class HlsMuxer(
     private val outputDirectory: File,
     private val callback: Callback,
-    private val orientationDegrees: Int = 0
+    private val orientationDegrees: Int = 0,
+    private val fps: Int = 30
 ) {
     companion object {
         private const val TAG = "HlsMuxer"
@@ -41,8 +42,7 @@ class HlsMuxer(
 
     // Configuration
     private var targetSegmentDurationUs: Long = DEFAULT_SEGMENT_DURATION_US
-    private var timescale: Int = 30000  // Default, updated from format
-    private var configuredFps: Int = 30  // Configured fps from user, used for VUI timing
+    private var timescale: Int = 30000  // Default, updated in addTrack() to fps * 1000
 
     // State
     private var state = State.UNINITIALIZED
@@ -55,9 +55,14 @@ class HlsMuxer(
     private var segmentStartTimeUs = -1L
     private var lastPresentationTimeUs = 0L
 
-    // Timestamp normalization - first timestamp becomes time 0
+    // Timestamp normalization - MediaCodec timestamps are device uptime, not starting from 0
     private var firstPresentationTimeUs = -1L
 
+    // Actual fps detection from frame timestamps
+    private var detectedFps: Int? = null
+    private var fpsDetectionSamples = mutableListOf<Long>()
+    private val FPS_DETECTION_SAMPLE_COUNT = 30
+
     private enum class State {
         UNINITIALIZED,
         INITIALIZED,
@@ -79,13 +84,21 @@ class HlsMuxer(
      * Normalizes a presentation timestamp to start from 0.
      * The first timestamp received becomes time 0, and all subsequent
      * timestamps are relative to that.
+     *
+     * This is necessary because MediaCodec timestamps are based on device uptime,
+     * not starting from 0. HLS players expect timestamps to start at or near 0.
      */
     private fun normalizeTimestamp(rawPresentationTimeUs: Long): Long {
         if (firstPresentationTimeUs < 0) {
             firstPresentationTimeUs = rawPresentationTimeUs
-            Log.d(TAG, "First timestamp: ${rawPresentationTimeUs}us, normalizing to 0")
+            Log.d(TAG, "First timestamp captured: ${rawPresentationTimeUs}us (${rawPresentationTimeUs / 1_000_000.0}s), normalizing to 0")
         }
-        return rawPresentationTimeUs - firstPresentationTimeUs
+        val normalized = rawPresentationTimeUs - firstPresentationTimeUs
+        // Log first few normalizations to debug
+        if (normalized < 1_000_000) { // First second
+            Log.d(TAG, "Timestamp: raw=${rawPresentationTimeUs}us -> normalized=${normalized}us")
+        }
+        return normalized
     }
 
     // ==================== Annex-B to AVCC Conversion ====================
@@ -213,15 +226,18 @@ class HlsMuxer(
      * Adds a track to the muxer.
      *
      * @param format The MediaFormat describing the track
-     * @param fps The configured frame rate (used for VUI timing, overrides format's fps)
      * @return Track index (always 0 for now, single video track)
      */
-    fun addTrack(format: MediaFormat, fps: Int = 30): Int {
+    fun addTrack(format: MediaFormat): Int {
         check(state == State.UNINITIALIZED) { "addTrack() must be called before start()" }
 
         trackFormat = format
-        configuredFps = fps
-        timescale = fps * 1000  // Use fps * 1000 for good precision
+
+        // Use fps * 1000 as timescale for good precision (1000 timescale units per frame).
+        // This ensures accurate sample durations without integer truncation issues.
+        // Note: ffprobe may report r_frame_rate based on timescale, so the backend
+        // should use the explicit framesPerSecond from the API mutation, not ffprobe.
+        timescale = fps * 1000
 
         state = State.INITIALIZED
 
@@ -229,7 +245,7 @@ class HlsMuxer(
         val formatHeight = try { format.getInteger(MediaFormat.KEY_HEIGHT) } catch (e: Exception) { -1 }
         Log.d(TAG, "Added track: ${format.getString(MediaFormat.KEY_MIME)}, " +
                 "encoder output: ${formatWidth}x${formatHeight}, " +
-                "configuredFps=$configuredFps, timescale=$timescale, orientation=$orientationDegrees°")
+                "fps=$fps, timescale=$timescale, orientation=$orientationDegrees°")
 
         return 0  // Single track, index 0
     }
@@ -241,16 +257,30 @@ class HlsMuxer(
         check(state == State.INITIALIZED) { "Must call addTrack() before start()" }
         val format = trackFormat ?: throw IllegalStateException("No track format")
 
-        // Create output directory if needed
+        // Create output directory if needed, with proper error handling
         if (!outputDirectory.exists()) {
-            outputDirectory.mkdirs()
+            val created = outputDirectory.mkdirs()
+            if (!created && !outputDirectory.exists()) {
+                throw IllegalStateException(
+                    "Failed to create output directory: ${outputDirectory.absolutePath}. " +
+                    "Parent exists: ${outputDirectory.parentFile?.exists()}, " +
+                    "Parent path: ${outputDirectory.parentFile?.absolutePath}"
+                )
+            }
+            Log.d(TAG, "Created output directory: ${outputDirectory.absolutePath}")
         }
 
         // Write init segment
         val initBytes = buildInitSegment(format)
         val initFile = File(outputDirectory, "init.mp4")
         FileOutputStream(initFile).use { it.write(initBytes) }
+
+        // Log frame rate metadata for debugging
+        val defaultSampleDuration = timescale / fps
         Log.d(TAG, "Created init segment: ${initFile.absolutePath} (${initBytes.size} bytes)")
+        Log.d(TAG, "Frame rate metadata: timescale=$timescale, fps=$fps, " +
+                "default_sample_duration=$defaultSampleDuration (ffprobe should calculate ${timescale}/${defaultSampleDuration}=${fps}fps)")
+
         callback.onInitSegmentReady(initFile)
 
         state = State.STARTED
@@ -273,13 +303,40 @@ class HlsMuxer(
         }
 
         val isKeyFrame = (bufferInfo.flags and MediaCodec.BUFFER_FLAG_KEY_FRAME) != 0
+        // Normalize timestamp to start from 0 (MediaCodec uses device uptime)
         val presentationTimeUs = normalizeTimestamp(bufferInfo.presentationTimeUs)
 
+        // Detect actual fps from first N samples
+        if (detectedFps == null) {
+            fpsDetectionSamples.add(presentationTimeUs)
+            if (fpsDetectionSamples.size >= FPS_DETECTION_SAMPLE_COUNT) {
+                val elapsed = fpsDetectionSamples.last() - fpsDetectionSamples.first()
+                if (elapsed > 0) {
+                    val actualFps = ((FPS_DETECTION_SAMPLE_COUNT - 1) * 1_000_000.0 / elapsed).toInt()
+                    detectedFps = actualFps
+                    if (kotlin.math.abs(actualFps - fps) > 5) {
+                        Log.w(TAG, "Actual fps ($actualFps) differs significantly from configured fps ($fps)! " +
+                                "This may cause processing issues if backend uses configured fps.")
+                    } else {
+                        Log.d(TAG, "Detected actual fps: $actualFps (configured: $fps)")
+                    }
+                }
+                fpsDetectionSamples.clear() // Free memory
+            }
+        }
+
         // Initialize segment start time
         if (segmentStartTimeUs < 0) {
             segmentStartTimeUs = presentationTimeUs
         }
 
+        // Update duration of previous sample BEFORE finalization check
+        // This ensures the last sample has correct duration when segment is finalized
+        if (pendingSamples.isNotEmpty()) {
+            val lastSample = pendingSamples.last()
+            lastSample.durationUs = presentationTimeUs - lastSample.presentationTimeUs
+        }
+
         // Check if we should finalize current segment (at keyframe boundaries)
         if (isKeyFrame && pendingSamples.isNotEmpty()) {
             val segmentDurationUs = presentationTimeUs - segmentStartTimeUs
@@ -298,12 +355,6 @@ class HlsMuxer(
         // Convert Annex-B (start codes) to AVCC (length prefixes)
         val data = convertAnnexBToAvcc(rawData)
 
-        // Update duration of previous sample
-        if (pendingSamples.isNotEmpty()) {
-            val lastSample = pendingSamples.last()
-            lastSample.durationUs = presentationTimeUs - lastSample.presentationTimeUs
-        }
-
         // Estimate duration (will be corrected by next sample)
         val estimatedDurationUs = if (lastPresentationTimeUs > 0) {
             presentationTimeUs - lastPresentationTimeUs
@@ -365,6 +416,7 @@ class HlsMuxer(
             val durationUs = (lastSample.presentationTimeUs - firstPts) + lastSample.durationUs
 
             Log.d(TAG, "Created segment $segmentIndex: samples=${pendingSamples.size}, " +
+                    "baseDecodeTime=${baseDecodeTimeUs}us (${baseDecodeTimeUs / 1_000_000.0}s), " +
                     "duration=${durationUs / 1000}ms, size=${fragmentBytes.size} bytes")
 
             callback.onMediaSegmentReady(segmentFile, segmentIndex, durationUs)
@@ -378,303 +430,6 @@ class HlsMuxer(
         }
     }
 
-    // ==================== SPS VUI Timing Injection ====================
-
-    /**
-     * Injects VUI timing parameters into an H.264 SPS NAL unit.
-     * This ensures proper frame rate detection by players/decoders.
-     *
-     * The SPS from MediaCodec lacks VUI timing info, causing tools like
-     * ffprobe to misinterpret the frame rate.
-     */
-    private fun injectVuiTiming(sps: ByteArray, fps: Int): ByteArray {
-        try {
-            val reader = BitReader(sps)
-            val writer = BitWriter()
-
-            // NAL header (1 byte: forbidden_zero_bit, nal_ref_idc, nal_unit_type)
-            writer.writeBits(reader.readBits(8), 8)
-
-            // profile_idc (1 byte)
-            val profileIdc = reader.readBits(8)
-            writer.writeBits(profileIdc, 8)
-
-            // constraint_set flags (1 byte)
-            writer.writeBits(reader.readBits(8), 8)
-
-            // level_idc (1 byte)
-            writer.writeBits(reader.readBits(8), 8)
-
-            // seq_parameter_set_id (ue(v))
-            copyExpGolomb(reader, writer)
-
-            // Profile-specific fields for High profile (100) and others
-            if (profileIdc == 100 || profileIdc == 110 || profileIdc == 122 ||
-                profileIdc == 244 || profileIdc == 44 || profileIdc == 83 ||
-                profileIdc == 86 || profileIdc == 118 || profileIdc == 128 ||
-                profileIdc == 138 || profileIdc == 139 || profileIdc == 134 ||
-                profileIdc == 135) {
-
-                // chroma_format_idc (ue(v))
-                val chromaFormatIdc = copyExpGolombAndReturn(reader, writer)
-
-                if (chromaFormatIdc == 3) {
-                    // separate_colour_plane_flag (1 bit)
-                    writer.writeBits(reader.readBits(1), 1)
-                }
-
-                // bit_depth_luma_minus8 (ue(v))
-                copyExpGolomb(reader, writer)
-
-                // bit_depth_chroma_minus8 (ue(v))
-                copyExpGolomb(reader, writer)
-
-                // qpprime_y_zero_transform_bypass_flag (1 bit)
-                writer.writeBits(reader.readBits(1), 1)
-
-                // seq_scaling_matrix_present_flag (1 bit)
-                val scalingMatrixFlag = reader.readBits(1)
-                writer.writeBits(scalingMatrixFlag, 1)
-
-                if (scalingMatrixFlag == 1) {
-                    // Skip scaling lists - this is complex, just copy remaining and give up
-                    Log.w(TAG, "SPS has scaling matrix, skipping VUI injection")
-                    return sps
-                }
-            }
-
-            // log2_max_frame_num_minus4 (ue(v))
-            copyExpGolomb(reader, writer)
-
-            // pic_order_cnt_type (ue(v))
-            val picOrderCntType = copyExpGolombAndReturn(reader, writer)
-
-            if (picOrderCntType == 0) {
-                // log2_max_pic_order_cnt_lsb_minus4 (ue(v))
-                copyExpGolomb(reader, writer)
-            } else if (picOrderCntType == 1) {
-                // delta_pic_order_always_zero_flag (1 bit)
-                writer.writeBits(reader.readBits(1), 1)
-                // offset_for_non_ref_pic (se(v))
-                copySignedExpGolomb(reader, writer)
-                // offset_for_top_to_bottom_field (se(v))
-                copySignedExpGolomb(reader, writer)
-                // num_ref_frames_in_pic_order_cnt_cycle (ue(v))
-                val numRefFrames = copyExpGolombAndReturn(reader, writer)
-                for (i in 0 until numRefFrames) {
-                    // offset_for_ref_frame[i] (se(v))
-                    copySignedExpGolomb(reader, writer)
-                }
-            }
-
-            // max_num_ref_frames (ue(v))
-            copyExpGolomb(reader, writer)
-
-            // gaps_in_frame_num_value_allowed_flag (1 bit)
-            writer.writeBits(reader.readBits(1), 1)
-
-            // pic_width_in_mbs_minus1 (ue(v))
-            copyExpGolomb(reader, writer)
-
-            // pic_height_in_map_units_minus1 (ue(v))
-            copyExpGolomb(reader, writer)
-
-            // frame_mbs_only_flag (1 bit)
-            val frameMbsOnlyFlag = reader.readBits(1)
-            writer.writeBits(frameMbsOnlyFlag, 1)
-
-            if (frameMbsOnlyFlag == 0) {
-                // mb_adaptive_frame_field_flag (1 bit)
-                writer.writeBits(reader.readBits(1), 1)
-            }
-
-            // direct_8x8_inference_flag (1 bit)
-            writer.writeBits(reader.readBits(1), 1)
-
-            // frame_cropping_flag (1 bit)
-            val frameCroppingFlag = reader.readBits(1)
-            writer.writeBits(frameCroppingFlag, 1)
-
-            if (frameCroppingFlag == 1) {
-                // frame_crop_left_offset, right, top, bottom (ue(v) each)
-                copyExpGolomb(reader, writer)
-                copyExpGolomb(reader, writer)
-                copyExpGolomb(reader, writer)
-                copyExpGolomb(reader, writer)
-            }
-
-            // vui_parameters_present_flag - we'll set this to 1 and add our VUI
-            val originalVuiFlag = reader.readBits(1)
-            writer.writeBits(1, 1)  // Set VUI present
-
-            // Write VUI parameters with timing info
-            writeVuiWithTiming(writer, fps, originalVuiFlag == 1, reader)
-
-            // Add RBSP trailing bits
-            writer.writeRbspTrailingBits()
-
-            val result = writer.toByteArray()
-            Log.d(TAG, "Injected VUI timing for ${fps}fps, SPS grew from ${sps.size} to ${result.size} bytes")
-            return result
-
-        } catch (e: Exception) {
-            Log.e(TAG, "Failed to inject VUI timing: ${e.message}, using original SPS")
-            return sps
-        }
-    }
-
-    /**
-     * Writes VUI parameters with timing info.
-     */
-    private fun writeVuiWithTiming(writer: BitWriter, fps: Int, hadVui: Boolean, reader: BitReader) {
-        // aspect_ratio_info_present_flag
-        writer.writeBits(0, 1)
-
-        // overscan_info_present_flag
-        writer.writeBits(0, 1)
-
-        // video_signal_type_present_flag
-        writer.writeBits(0, 1)
-
-        // chroma_loc_info_present_flag
-        writer.writeBits(0, 1)
-
-        // timing_info_present_flag = 1
-        writer.writeBits(1, 1)
-
-        // num_units_in_tick (32 bits) = 1
-        writer.writeBits(1, 32)
-
-        // time_scale (32 bits) = fps * 2 (because each frame = 2 field counts)
-        writer.writeBits(fps * 2, 32)
-
-        // fixed_frame_rate_flag = 1
-        writer.writeBits(1, 1)
-
-        // nal_hrd_parameters_present_flag
-        writer.writeBits(0, 1)
-
-        // vcl_hrd_parameters_present_flag
-        writer.writeBits(0, 1)
-
-        // pic_struct_present_flag
-        writer.writeBits(0, 1)
-
-        // bitstream_restriction_flag
-        writer.writeBits(0, 1)
-    }
-
-    // ==================== Bit Manipulation Helpers ====================
-
-    /**
-     * Bit-level reader for parsing H.264 NAL units.
-     */
-    private class BitReader(private val data: ByteArray) {
-        private var bytePos = 0
-        private var bitPos = 0
-
-        fun readBits(count: Int): Int {
-            var result = 0
-            for (i in 0 until count) {
-                if (bytePos >= data.size) throw IllegalStateException("End of data")
-                val bit = (data[bytePos].toInt() shr (7 - bitPos)) and 1
-                result = (result shl 1) or bit
-                bitPos++
-                if (bitPos == 8) {
-                    bitPos = 0
-                    bytePos++
-                }
-            }
-            return result
-        }
-
-        fun readExpGolomb(): Int {
-            var leadingZeros = 0
-            while (readBits(1) == 0) {
-                leadingZeros++
-                if (leadingZeros > 31) throw IllegalStateException("Invalid exp-golomb")
-            }
-            if (leadingZeros == 0) return 0
-            val suffix = readBits(leadingZeros)
-            return (1 shl leadingZeros) - 1 + suffix
-        }
-
-        fun readSignedExpGolomb(): Int {
-            val code = readExpGolomb()
-            return if (code % 2 == 0) -(code / 2) else (code + 1) / 2
-        }
-    }
-
-    /**
-     * Bit-level writer for constructing H.264 NAL units.
-     */
-    private class BitWriter {
-        private val bytes = mutableListOf<Byte>()
-        private var currentByte = 0
-        private var bitPos = 0
-
-        fun writeBits(value: Int, count: Int) {
-            for (i in count - 1 downTo 0) {
-                val bit = (value shr i) and 1
-                currentByte = (currentByte shl 1) or bit
-                bitPos++
-                if (bitPos == 8) {
-                    bytes.add(currentByte.toByte())
-                    currentByte = 0
-                    bitPos = 0
-                }
-            }
-        }
-
-        fun writeExpGolomb(value: Int) {
-            val code = value + 1
-            val bits = 32 - Integer.numberOfLeadingZeros(code)
-            // Write leading zeros
-            for (i in 0 until bits - 1) {
-                writeBits(0, 1)
-            }
-            // Write the code
-            writeBits(code, bits)
-        }
-
-        fun writeSignedExpGolomb(value: Int) {
-            val code = if (value <= 0) -2 * value else 2 * value - 1
-            writeExpGolomb(code)
-        }
-
-        fun writeRbspTrailingBits() {
-            writeBits(1, 1)  // rbsp_stop_one_bit
-            while (bitPos != 0) {
-                writeBits(0, 1)  // rbsp_alignment_zero_bit
-            }
-        }
-
-        fun toByteArray(): ByteArray {
-            // Flush remaining bits
-            if (bitPos > 0) {
-                currentByte = currentByte shl (8 - bitPos)
-                bytes.add(currentByte.toByte())
-            }
-            return bytes.toByteArray()
-        }
-    }
-
-    private fun copyExpGolomb(reader: BitReader, writer: BitWriter) {
-        val value = reader.readExpGolomb()
-        writer.writeExpGolomb(value)
-    }
-
-    private fun copyExpGolombAndReturn(reader: BitReader, writer: BitWriter): Int {
-        val value = reader.readExpGolomb()
-        writer.writeExpGolomb(value)
-        return value
-    }
-
-    private fun copySignedExpGolomb(reader: BitReader, writer: BitWriter) {
-        val value = reader.readSignedExpGolomb()
-        writer.writeSignedExpGolomb(value)
-    }
-
     // ==================== Init Segment Building ====================
 
     /**
@@ -684,19 +439,11 @@ class HlsMuxer(
         val width = format.getInteger(MediaFormat.KEY_WIDTH)
         val height = format.getInteger(MediaFormat.KEY_HEIGHT)
 
-        val rawSps = format.getByteBuffer("csd-0")?.let { extractNalUnit(it) }
+        val sps = format.getByteBuffer("csd-0")?.let { extractNalUnit(it) }
             ?: throw IllegalArgumentException("Missing SPS (csd-0)")
         val pps = format.getByteBuffer("csd-1")?.let { extractNalUnit(it) }
             ?: throw IllegalArgumentException("Missing PPS (csd-1)")
 
-        Log.d(TAG, "Original SPS size: ${rawSps.size} bytes, PPS size: ${pps.size} bytes")
-        Log.d(TAG, "Original SPS hex: ${rawSps.joinToString("") { "%02x".format(it) }}")
-
-        // Inject VUI timing info into SPS using configured fps (not encoder output format fps)
-        val sps = injectVuiTiming(rawSps, configuredFps)
-        Log.d(TAG, "Modified SPS size: ${sps.size} bytes")
-        Log.d(TAG, "Modified SPS hex: ${sps.joinToString("") { "%02x".format(it) }}")
-
         val output = ByteArrayOutputStream()
 
         // ftyp
@@ -797,56 +544,91 @@ class HlsMuxer(
         dos.writeShort(0)        // volume (0 for video)
         dos.writeShort(0)        // reserved
 
-        // Rotation matrix
-        writeRotationMatrix(dos)
+        // Rotation matrix based on orientationDegrees
+        writeRotationMatrix(dos, width, height)
 
-        // Display dimensions should be post-rotation dimensions
-        // For 90° or 270° rotation, swap width and height
+        // For 90° and 270° rotations, the display dimensions are swapped
+        // The tkhd width/height represent the final display size after rotation
         val (displayWidth, displayHeight) = when (orientationDegrees) {
-            90, 270 -> height to width
-            else -> width to height
+            90, 270 -> Pair(height, width)
+            else -> Pair(width, height)
         }
         dos.writeInt(displayWidth shl 16)   // width (16.16 fixed point)
         dos.writeInt(displayHeight shl 16)  // height (16.16 fixed point)
 
-        Log.d(TAG, "tkhd: encoded=${width}x${height}, display=${displayWidth}x${displayHeight}, rotation=$orientationDegrees")
+        Log.d(TAG, "tkhd: encoder=${width}x${height}, display=${displayWidth}x${displayHeight}, rotation=$orientationDegrees")
 
         return wrapBox("tkhd", output.toByteArray())
     }
 
     /**
      * Writes the 3x3 transformation matrix for video rotation.
+     * The matrix is applied to rotate the video content for correct display.
+     *
+     * Matrix format in tkhd box (all values in fixed-point):
+     * | a  b  u |   where a,b,c,d are 16.16 fixed-point
+     * | c  d  v |   and u,v are 2.30 fixed-point (always 0)
+     * | x  y  w |   x,y are 16.16, w is 2.30 (always 1.0)
+     *
+     * For rotation by θ: a=cos(θ), b=sin(θ), c=-sin(θ), d=cos(θ)
+     * Translation (x,y) keeps the rotated video in the visible area.
      */
-    private fun writeRotationMatrix(dos: DataOutputStream) {
+    private fun writeRotationMatrix(dos: DataOutputStream, width: Int, height: Int) {
+        // Fixed-point constants
         val one = 0x00010000      // 1.0 in 16.16
-        val negOne = 0xFFFF0000.toInt()  // -1.0 in 16.16
+        val negOne = -0x00010000  // -1.0 in 16.16 (will be written as unsigned)
         val w = 0x40000000        // 1.0 in 2.30
 
-        // For 270° device orientation (landscape-right), apply 90° CW rotation
-        // For 90° device orientation (landscape-left), apply 270° CW rotation
-        val a: Int
-        val b: Int
-        val c: Int
-        val d: Int
-
         when (orientationDegrees) {
-            90 -> { a = 0; b = negOne; c = one; d = 0 }
-            180 -> { a = negOne; b = 0; c = 0; d = negOne }
-            270 -> { a = 0; b = one; c = negOne; d = 0 }
-            else -> { a = one; b = 0; c = 0; d = one }
-        }
-
-        dos.writeInt(a)
-        dos.writeInt(b)
+            90 -> {
+                // 90° rotation: x' = y, y' = -x + width
+                dos.writeInt(0)              // a = 0
+                dos.writeInt(negOne)         // b = -1
                 dos.writeInt(0)              // u = 0
-        dos.writeInt(c)
-        dos.writeInt(d)
+                dos.writeInt(one)            // c = 1
+                dos.writeInt(0)              // d = 0
                 dos.writeInt(0)              // v = 0
-        dos.writeInt(0)     // tx = 0
-        dos.writeInt(0)     // ty = 0
-        dos.writeInt(w)     // w = 1.0
-
-        Log.d(TAG, "Rotation matrix for $orientationDegrees°")
+                dos.writeInt(0)              // x = 0
+                dos.writeInt(width shl 16)   // y = width (translation)
+                dos.writeInt(w)              // w = 1
+            }
+            180 -> {
+                // 180° rotation
+                dos.writeInt(negOne)         // a = -1
+                dos.writeInt(0)              // b = 0
+                dos.writeInt(0)              // u = 0
+                dos.writeInt(0)              // c = 0
+                dos.writeInt(negOne)         // d = -1
+                dos.writeInt(0)              // v = 0
+                dos.writeInt(width shl 16)   // x = width (translation)
+                dos.writeInt(height shl 16)  // y = height (translation)
+                dos.writeInt(w)              // w = 1
+            }
+            270 -> {
+                // 270° rotation: x' = -y + height, y' = x
+                dos.writeInt(0)              // a = 0
+                dos.writeInt(one)            // b = 1
+                dos.writeInt(0)              // u = 0
+                dos.writeInt(negOne)         // c = -1
+                dos.writeInt(0)              // d = 0
+                dos.writeInt(0)              // v = 0
+                dos.writeInt(height shl 16)  // x = height (translation)
+                dos.writeInt(0)              // y = 0
+                dos.writeInt(w)              // w = 1
+            }
+            else -> {
+                // 0° or unknown: identity matrix
+                dos.writeInt(one)   // a = 1
+                dos.writeInt(0)     // b = 0
+                dos.writeInt(0)     // u = 0
+                dos.writeInt(0)     // c = 0
+                dos.writeInt(one)   // d = 1
+                dos.writeInt(0)     // v = 0
+                dos.writeInt(0)     // x = 0
+                dos.writeInt(0)     // y = 0
+                dos.writeInt(w)     // w = 1
+            }
+        }
     }
 
     private fun buildMdiaBox(width: Int, height: Int, sps: ByteArray, pps: ByteArray): ByteArray {
@@ -933,7 +715,7 @@ class HlsMuxer(
     private fun buildStblBox(width: Int, height: Int, sps: ByteArray, pps: ByteArray): ByteArray {
         val content = ByteArrayOutputStream()
         content.write(buildStsdBox(width, height, sps, pps))
-        content.write(buildEmptySttsBox())
+        content.write(buildSttsBox())  // Contains default timing for ffprobe frame rate detection
         content.write(buildEmptyStscBox())
         content.write(buildEmptyStszBox())
         content.write(buildEmptyStcoBox())
@@ -979,10 +761,9 @@ class HlsMuxer(
         val output = ByteArrayOutputStream()
         val dos = DataOutputStream(output)
 
-        // SPS layout: [0]=NAL header (0x67), [1]=profile_idc, [2]=constraint_flags, [3]=level_idc
-        val profileIdc = if (sps.size > 1) sps[1].toInt() and 0xFF else 0x42
-        val profileCompat = if (sps.size > 2) sps[2].toInt() and 0xFF else 0x00
-        val levelIdc = if (sps.size > 3) sps[3].toInt() and 0xFF else 0x1F
+        val profileIdc = if (sps.isNotEmpty()) sps[0].toInt() and 0xFF else 0x42
+        val profileCompat = if (sps.size > 1) sps[1].toInt() and 0xFF else 0x00
+        val levelIdc = if (sps.size > 2) sps[2].toInt() and 0xFF else 0x1F
 
         dos.writeByte(1)            // configuration version
         dos.writeByte(profileIdc)   // AVC profile
@@ -1001,11 +782,21 @@ class HlsMuxer(
         return wrapBox("avcC", output.toByteArray())
     }
 
-    private fun buildEmptySttsBox(): ByteArray {
+    private fun buildSttsBox(): ByteArray {
         val output = ByteArrayOutputStream()
         val dos = DataOutputStream(output)
+
+        // For fragmented MP4, stts is normally empty as timing is in trun boxes.
+        // However, ffprobe uses stts to calculate r_frame_rate when present.
+        // We add a single entry with the default sample duration so ffprobe
+        // can derive: r_frame_rate = timescale / sample_delta = 30000/1000 = 30
+        val defaultSampleDuration = timescale / fps
+
         dos.writeInt(0)  // version & flags
-        dos.writeInt(0)  // entry count
+        dos.writeInt(1)  // entry count (1 entry for default timing)
+        dos.writeInt(1)  // sample_count (indicates this is the default duration)
+        dos.writeInt(defaultSampleDuration)  // sample_delta in timescale units
+
         return wrapBox("stts", output.toByteArray())
     }
 
@@ -1042,9 +833,10 @@ class HlsMuxer(
         val output = ByteArrayOutputStream()
         val dos = DataOutputStream(output)
 
-        // Default sample duration: timescale / fps
-        // Since timescale = fps * 1000, duration = 1000 for any fps
-        val defaultSampleDuration = 1000
+        // Calculate default sample duration so ffprobe can derive correct fps
+        // fps = timescale / default_sample_duration
+        // At 30fps with timescale=30000: duration=1000, ffprobe calculates 30000/1000=30
+        val defaultSampleDuration = timescale / fps
 
         dos.writeInt(0)  // version & flags
         dos.writeInt(1)  // track ID
@@ -1161,13 +953,10 @@ class HlsMuxer(
         dos.writeInt(samples.size)
         dos.writeInt(dataOffset)
 
-        // Use constant duration based on configured fps for consistent frame rate
-        // This ensures ffprobe reports correct fps instead of calculating from variable timing
-        val constantDuration = timescale / configuredFps  // e.g., 30000/30 = 1000 ticks
-        Log.d(TAG, "Writing ${samples.size} samples with constant duration=${constantDuration} ticks (${configuredFps}fps)")
-
         for (sample in samples) {
-            dos.writeInt(constantDuration)
+            // Convert duration to timescale units
+            val durationInTimescale = ((sample.durationUs * timescale) / 1_000_000).toInt()
+            dos.writeInt(durationInTimescale)
             dos.writeInt(sample.data.size)
             dos.writeInt(buildSampleFlags(sample.isKeyFrame))
         }

package/android/src/main/java/com/mrousavy/camera/core/RecordingSession.kt

@@ -44,7 +44,14 @@ class RecordingSession(
 
   data class Video(val path: String, val durationMs: Long, val size: Size)
 
-  private val outputPath: File = File(filePath)
+  // Strip file:// prefix if present (expo-file-system returns URIs with this prefix)
+  private val outputPath: File = File(
+    if (filePath.startsWith("file://")) {
+      filePath.removePrefix("file://")
+    } else {
+      filePath
+    }
+  )
 
   private val bitRate = getBitRate()