wip: add vui timing injection, receive the requested fps from camera in rn layer, normalize timestamp

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) → 270° hint
-      // - Clockwise (ROTATION_270) → 90° hint
+      // - Counter-clockwise (ROTATION_90) → 90° hint
+      // - Clockwise (ROTATION_270) → 270° 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_RIGHT
+        Surface.ROTATION_90 -> Orientation.LANDSCAPE_LEFT
         Surface.ROTATION_180 -> Orientation.PORTRAIT_UPSIDE_DOWN
-        Surface.ROTATION_270 -> Orientation.LANDSCAPE_LEFT
+        Surface.ROTATION_270 -> Orientation.LANDSCAPE_RIGHT
         else -> Orientation.PORTRAIT
       }
 
@@ -448,7 +448,7 @@ class CameraSession(private val context: Context, private val cameraManager: Cam
         enableAudio,
         fps,
         videoOutput.enableHdr,
-        orientation,
+        recordingOrientation,
         options,
         filePath,
         callback,

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

@@ -20,7 +20,8 @@ import java.io.File
  */
 class FragmentedRecordingManager(
     private val encoder: MediaCodec,
-    private val muxer: HlsMuxer
+    private val muxer: HlsMuxer,
+    private val configuredFps: Int
 ) : MediaCodec.Callback(), ChunkedRecorderInterface {
 
     companion object {
@@ -39,17 +40,21 @@ class FragmentedRecordingManager(
             segmentDurationSeconds: Int = DEFAULT_SEGMENT_DURATION_SECONDS
         ): FragmentedRecordingManager {
             val mimeType = options.videoCodec.toMimeType()
-            val cameraOrientationDegrees = cameraOrientation.toDegrees()
-            val recordingOrientationDegrees = (options.orientation ?: Orientation.PORTRAIT).toDegrees()
+            // Use cameraOrientation from Android (computed from device rotation)
+            // instead of options.orientation from JS which may be stale
+            val recordingOrientationDegrees = cameraOrientation.toDegrees()
 
-            // Use size dimensions directly - the encoder output format will have the actual dimensions
-            // Don't swap based on orientation here; the camera pipeline handles that
-            val width = size.width
-            val height = size.height
+            // Swap dimensions based on orientation - same logic as ChunkedRecordingManager
+            // When camera is in landscape orientation, we need to swap width/height for the encoder
+            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}, " +
-                    "cameraOrientation: $cameraOrientation ($cameraOrientationDegrees°), " +
-                    "recordingOrientation: $recordingOrientationDegrees°")
+                    "encoder size: ${width}x${height}, " +
+                    "orientation: $cameraOrientation ($recordingOrientationDegrees°)")
 
             val format = MediaFormat.createVideoFormat(mimeType, width, height)
             val codec = MediaCodec.createEncoderByType(mimeType)
@@ -84,9 +89,9 @@ class FragmentedRecordingManager(
             )
             muxer.setSegmentDuration(segmentDurationSeconds * 1_000_000L)
 
-            Log.d(TAG, "Created HlsMuxer with orientation: $recordingOrientationDegrees degrees")
+            Log.d(TAG, "Created HlsMuxer with orientation: $recordingOrientationDegrees degrees, fps: $effectiveFps")
 
-            return FragmentedRecordingManager(codec, muxer)
+            return FragmentedRecordingManager(codec, muxer, effectiveFps)
         }
     }
 
@@ -166,7 +171,8 @@ class FragmentedRecordingManager(
         synchronized(this) {
             Log.i(TAG, "Output format changed: $format")
 
-            trackIndex = muxer.addTrack(format)
+            // Pass configured fps to muxer (not the encoder's output format fps which may differ)
+            trackIndex = muxer.addTrack(format, configuredFps)
             muxer.start()
             muxerStarted = true
         }

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

@@ -42,6 +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
 
     // State
     private var state = State.UNINITIALIZED
@@ -54,6 +55,9 @@ class HlsMuxer(
     private var segmentStartTimeUs = -1L
     private var lastPresentationTimeUs = 0L
 
+    // Timestamp normalization - first timestamp becomes time 0
+    private var firstPresentationTimeUs = -1L
+
     private enum class State {
         UNINITIALIZED,
         INITIALIZED,
@@ -69,6 +73,21 @@ class HlsMuxer(
         val isKeyFrame: Boolean
     )
 
+    // ==================== Timestamp Normalization ====================
+
+    /**
+     * Normalizes a presentation timestamp to start from 0.
+     * The first timestamp received becomes time 0, and all subsequent
+     * timestamps are relative to that.
+     */
+    private fun normalizeTimestamp(rawPresentationTimeUs: Long): Long {
+        if (firstPresentationTimeUs < 0) {
+            firstPresentationTimeUs = rawPresentationTimeUs
+            Log.d(TAG, "First timestamp: ${rawPresentationTimeUs}us, normalizing to 0")
+        }
+        return rawPresentationTimeUs - firstPresentationTimeUs
+    }
+
     // ==================== Annex-B to AVCC Conversion ====================
 
     /**
@@ -194,19 +213,14 @@ 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): Int {
+    fun addTrack(format: MediaFormat, fps: Int = 30): Int {
         check(state == State.UNINITIALIZED) { "addTrack() must be called before start()" }
 
         trackFormat = format
-
-        // Extract timescale from frame rate
-        val fps = try {
-            format.getInteger(MediaFormat.KEY_FRAME_RATE)
-        } catch (e: Exception) {
-            30
-        }
+        configuredFps = fps
         timescale = fps * 1000  // Use fps * 1000 for good precision
 
         state = State.INITIALIZED
@@ -215,7 +229,7 @@ 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}, " +
-                "timescale=$timescale, orientation=$orientationDegrees°")
+                "configuredFps=$configuredFps, timescale=$timescale, orientation=$orientationDegrees°")
 
         return 0  // Single track, index 0
     }
@@ -259,7 +273,7 @@ class HlsMuxer(
         }
 
         val isKeyFrame = (bufferInfo.flags and MediaCodec.BUFFER_FLAG_KEY_FRAME) != 0
-        val presentationTimeUs = bufferInfo.presentationTimeUs
+        val presentationTimeUs = normalizeTimestamp(bufferInfo.presentationTimeUs)
 
         // Initialize segment start time
         if (segmentStartTimeUs < 0) {
@@ -364,6 +378,303 @@ 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 ====================
 
     /**
@@ -373,11 +684,19 @@ class HlsMuxer(
         val width = format.getInteger(MediaFormat.KEY_WIDTH)
         val height = format.getInteger(MediaFormat.KEY_HEIGHT)
 
-        val sps = format.getByteBuffer("csd-0")?.let { extractNalUnit(it) }
+        val rawSps = 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
@@ -478,40 +797,56 @@ class HlsMuxer(
         dos.writeShort(0)        // volume (0 for video)
         dos.writeShort(0)        // reserved
 
-        // Rotation matrix - use identity and rely on correct dimensions from encoder
-        // The encoder output format already has the correct dimensions for the content
+        // Rotation matrix
         writeRotationMatrix(dos)
 
-        // Use dimensions as-is from encoder output format
-        dos.writeInt(width shl 16)   // width (16.16 fixed point)
-        dos.writeInt(height shl 16)  // height (16.16 fixed point)
+        // Display dimensions should be post-rotation dimensions
+        // For 90° or 270° rotation, swap width and height
+        val (displayWidth, displayHeight) = when (orientationDegrees) {
+            90, 270 -> height to width
+            else -> width to 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: ${width}x${height}, rotation=$orientationDegrees")
+        Log.d(TAG, "tkhd: encoded=${width}x${height}, display=${displayWidth}x${displayHeight}, rotation=$orientationDegrees")
 
         return wrapBox("tkhd", output.toByteArray())
     }
 
     /**
      * Writes the 3x3 transformation matrix for video rotation.
-     * Uses simple rotation values - the encoder already outputs correctly oriented frames.
      */
     private fun writeRotationMatrix(dos: DataOutputStream) {
-        // Fixed-point constants
-        val one = 0x00010000      // 1.0 in 16.16
-        val w = 0x40000000        // 1.0 in 2.30
+        val one = 0x00010000       // 1.0 in 16.16
+        val negOne = 0xFFFF0000.toInt()  // -1.0 in 16.16
+        val w = 0x40000000         // 1.0 in 2.30
 
-        // Identity matrix - no transformation
-        // Most HLS players handle rotation via the dimensions themselves
-        // or we can add rotation metadata separately if needed
-        dos.writeInt(one)   // a = 1
-        dos.writeInt(0)     // b = 0
+        // 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)
         dos.writeInt(0)     // u = 0
-        dos.writeInt(0)     // c = 0
-        dos.writeInt(one)   // d = 1
+        dos.writeInt(c)
+        dos.writeInt(d)
         dos.writeInt(0)     // v = 0
-        dos.writeInt(0)     // x = 0
-        dos.writeInt(0)     // y = 0
-        dos.writeInt(w)     // w = 1
+        dos.writeInt(0)     // tx = 0
+        dos.writeInt(0)     // ty = 0
+        dos.writeInt(w)     // w = 1.0
+
+        Log.d(TAG, "Rotation matrix for $orientationDegrees°")
     }
 
     private fun buildMdiaBox(width: Int, height: Int, sps: ByteArray, pps: ByteArray): ByteArray {
@@ -644,9 +979,10 @@ class HlsMuxer(
         val output = ByteArrayOutputStream()
         val dos = DataOutputStream(output)
 
-        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
+        // 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
 
         dos.writeByte(1)            // configuration version
         dos.writeByte(profileIdc)   // AVC profile
@@ -706,10 +1042,14 @@ 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
+
         dos.writeInt(0)  // version & flags
         dos.writeInt(1)  // track ID
         dos.writeInt(1)  // default sample description index
-        dos.writeInt(0)  // default sample duration
+        dos.writeInt(defaultSampleDuration)  // default sample duration
         dos.writeInt(0)  // default sample size
         dos.writeInt(0)  // default sample flags
 
@@ -821,10 +1161,13 @@ 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) {
-            // Convert duration to timescale units
-            val durationInTimescale = ((sample.durationUs * timescale) / 1_000_000).toInt()
-            dos.writeInt(durationInTimescale)
+            dos.writeInt(constantDuration)
             dos.writeInt(sample.data.size)
             dos.writeInt(buildSampleFlags(sample.isKeyFrame))
         }