From c0b352dc1dd8a8cfd5dbf016e447f321e239bd2a Mon Sep 17 00:00:00 2001
From: Loewy <loewymalkov@gmail.com>
Date: Tue, 30 Dec 2025 15:01:41 -0500
Subject: [PATCH] fix fps (alter tfhd and trun size, add logs

---
 .../java/com/mrousavy/camera/core/HlsMuxer.kt | 33 ++++++++++++++-----
 1 file changed, 24 insertions(+), 9 deletions(-)

diff --git a/package/android/src/main/java/com/mrousavy/camera/core/HlsMuxer.kt b/package/android/src/main/java/com/mrousavy/camera/core/HlsMuxer.kt
index 7b9787e..1e41589 100644
--- a/package/android/src/main/java/com/mrousavy/camera/core/HlsMuxer.kt
+++ b/package/android/src/main/java/com/mrousavy/camera/core/HlsMuxer.kt
@@ -885,9 +885,11 @@ class HlsMuxer(
     ): ByteArray {
         // Calculate sizes to determine data offset
         val mfhdBox = buildMfhdBox(sequenceNumber)
-        val tfhdSize = 8 + 8   // box header + content (version/flags + track_id)
+        // tfhd: 8 header + 4 version/flags + 4 track_id + 4 duration + 4 size + 4 flags = 28 bytes
+        val tfhdSize = 8 + 20
         val tfdtSize = 8 + 12  // box header + version 1 content
-        val trunSize = 8 + 12 + (samples.size * 12)  // header + fixed + per-sample (no composition offset)
+        // trun: 8 header + 12 fixed + per-sample (size + flags only, no duration)
+        val trunSize = 8 + 12 + (samples.size * 8)
         val trafSize = 8 + tfhdSize + tfdtSize + trunSize
         val moofSize = 8 + mfhdBox.size + trafSize
 
@@ -922,9 +924,21 @@ class HlsMuxer(
         val output = ByteArrayOutputStream()
         val dos = DataOutputStream(output)
 
-        // Flags: default-base-is-moof (0x020000)
-        dos.writeInt(0x00020000)
+        // Calculate default sample duration for this fragment
+        // This helps ffprobe calculate correct frame rate when reading via HLS
+        val defaultSampleDuration = timescale / fps  // e.g., 30000/30 = 1000
+
+        // Match iOS AVFoundation's tfhd structure (28 bytes total)
+        // Flags: default-base-is-moof (0x020000) + default-sample-duration (0x000008)
+        //        + default-sample-size (0x000010) + default-sample-flags (0x000020)
+        val flags = 0x00020000 or 0x000008 or 0x000010 or 0x000020
+        dos.writeInt(flags)
         dos.writeInt(1)  // track ID
+        dos.writeInt(defaultSampleDuration)  // default sample duration in timescale units
+        dos.writeInt(0)  // default sample size (0 = variable, specified in trun)
+        dos.writeInt(0x01010000)  // default sample flags (non-keyframe, depends on others)
+
+        Log.d(TAG, "tfhd: default_sample_duration=$defaultSampleDuration (timescale=$timescale, fps=$fps)")
 
         return wrapBox("tfhd", output.toByteArray())
     }
@@ -947,16 +961,17 @@ class HlsMuxer(
         val output = ByteArrayOutputStream()
         val dos = DataOutputStream(output)
 
-        // Flags: data-offset + sample-duration + sample-size + sample-flags
-        val flags = 0x000001 or 0x000100 or 0x000200 or 0x000400
+        // Flags: data-offset + sample-size + sample-flags
+        // NOTE: We intentionally OMIT sample-duration (0x000100) so ffprobe uses
+        // the default_sample_duration from tfhd instead of per-sample durations.
+        // This ensures consistent frame rate calculation via HLS.
+        val flags = 0x000001 or 0x000200 or 0x000400
         dos.writeInt(flags)
         dos.writeInt(samples.size)
         dos.writeInt(dataOffset)
 
         for (sample in samples) {
-            // Convert duration to timescale units
-            val durationInTimescale = ((sample.durationUs * timescale) / 1_000_000).toInt()
-            dos.writeInt(durationInTimescale)
+            // No duration - using default from tfhd
             dos.writeInt(sample.data.size)
             dos.writeInt(buildSampleFlags(sample.isKeyFrame))
         }