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

[Zhao Zhili via ffmpeg-devel <ffmpeg-devel@ffmpeg.org>]

> On Nov 21, 2025, at 12:37, 树 via ffmpeg-devel <ffmpeg-devel@ffmpeg.org> wrote:
> 
> 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
> &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;* &nbsp; &nbsp; &nbsp;TID &nbsp; &nbsp; = 1
> &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; */
> &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;

Corrupted text. Please note qq email web client doesn’t support plain text.

Could you send a PR on https://code.ffmpeg.org/FFmpeg/FFmpeg?

> 
> 
> ## 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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