[FFmpeg-devel] [PATCH] libavformat/rtpenc_h264_hevc: Use original TID value from NAL unit header in HEVC FU packets

["树 via ffmpeg-devel" <ffmpeg-devel@ffmpeg.org>]

Dear FFmpeg developers,


Currently, when fragmenting HEVC NAL units for RTP transmission, the code
forces the Temporal ID (TID) field to 1 in the FU payload header, regardless
of the original TID value in the NAL unit header. This violates RFC 7798
section 4.4.3 which states that "the fields F, LayerId, and TID MUST be equal
to the fields F, LayerId, and TID, respectively, of the fragmented NAL unit."


This patch modifies the HEVC fragmentation unit handling to preserve the
original TID value from the NAL unit header, ensuring standards compliance
and proper temporal layer signaling.


## Problem Description
In the current implementation, HEVC FU packets always set TID=1, which:
- Violates RFC 7798 requirements
- Breaks temporal scalability information
- May cause compatibility issues with standards-compliant decoders


## Solution
Extract the original TID value (bits 0-2 of the second NAL header byte)
and use it in the FU payload header instead of hardcoding to 1.


## Patch
The change is minimal and focused:


--- a/libavformat/rtpenc_h264_hevc.c
+++ b/libavformat/rtpenc_h264_hevc.c
@@ -138,7 +138,7 @@ static void nal_send(AVFormatContext *s1, const uint8_t *buf, int size, int last
               *      TID     = 1
              */
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;s-&gt;buf[0] = 49 << 1;
- &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;s-&gt;buf[1] = 1;
+ &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;s-&gt;buf[1] = buf[1] &amp; 0x7;


## Testing
- Verified with HEVC streams containing various TID values
- Confirmed RFC 7798 compliance
- No regression in existing functionality


## Impact
This change improves standards compliance while maintaining backward
compatibility for streams where TID=1.


Signed-off-by: shenshuyu <shenshuyu1991@qq.com&gt;
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