[FFmpeg-devel] [PATCH] avformat/hlsenc: fix CODECS Attribute hard code in hevc EXT-X-STREAM-INF

[Jack Lau]

> On Mar 2, 2025, at 15:47, Jack Lau via ffmpeg-devel <ffmpeg-devel at ffmpeg.org> wrote:
> 
> fix ticket: 10786
> parse the SPS from extradata and get profile_compatibility, tier, constraints which was been hard code before.
> 
> HEVC CODECS Attribute reference to: ISO/IEC14496-15
> Signed-off-by: Jack Lau <jacklau1222 at qq.com>
> ---
> libavformat/hlsenc.c | 37 ++++++++++++++++++++++++++++++++++---
> 1 file changed, 34 insertions(+), 3 deletions(-)
> 
> diff --git a/libavformat/hlsenc.c b/libavformat/hlsenc.c
> index 6148685f40..be7a78021a 100644
> --- a/libavformat/hlsenc.c
> +++ b/libavformat/hlsenc.c
> @@ -379,7 +379,10 @@ static void write_codec_attr(AVStream *st, VariantStream *vs)
>     } else if (st->codecpar->codec_id == AV_CODEC_ID_HEVC) {
>         uint8_t *data = st->codecpar->extradata;
>         int profile = AV_PROFILE_UNKNOWN;
> +        uint32_t profile_compatibility = AV_PROFILE_UNKNOWN; 
> +        char tier = '0';
>         int level = AV_LEVEL_UNKNOWN;
> +        char constraints[5] = "0";
> 
>         if (st->codecpar->profile != AV_PROFILE_UNKNOWN)
>             profile = st->codecpar->profile;
> @@ -393,6 +396,8 @@ static void write_codec_attr(AVStream *st, VariantStream *vs)
>                 uint8_t *rbsp_buf;
>                 int remain_size = 0;
>                 int rbsp_size = 0;
> +                uint32_t profile_compatibility_flags = 0;
> +                uint8_t high_nibble = 0;
>                 /* skip start code + nalu header */
>                 data += 6;
>                 /* process by reference General NAL unit syntax */
> @@ -406,8 +411,31 @@ static void write_codec_attr(AVStream *st, VariantStream *vs)
>                 }
>                 /* skip sps_video_parameter_set_id   u(4),
>                  *      sps_max_sub_layers_minus1    u(3),
> -                 *  and sps_temporal_id_nesting_flag u(1) */
> +                 *  and sps_temporal_id_nesting_flag u(1) 
> +                 * 
> +                 * TIER represents the general_tier_flag, with 'L' indicating the flag is 0,
> +                 * and 'H' indicating the flag is 1
> +                 */
> +                tier = (int)(rbsp_buf[1] & 0x20) == 0 ? 'L' : 'H';
>                 profile = rbsp_buf[1] & 0x1f;
> +                /* PROFILE_COMPATIBILITY is general_profile_compatibility_flags, but in reverse bit order,
> +                 * in a hexadecimal representation (leading zeroes may be omitted).
> +                 */
> +                profile_compatibility_flags = (rbsp_buf[2] << 24) | (rbsp_buf[3] << 16) | (rbsp_buf[4] << 8) | rbsp_buf[5];
> +                /* revise these bits to get the profile compatibility value */
> +                for (int i = 0; i < 32; i++) {
> +                    profile_compatibility = (profile_compatibility << 1) | (profile_compatibility_flags & 1);
> +                    profile_compatibility_flags >>= 1;
> +                }
> +                /* skip 8 + 8 + 32
> +                 * CONSTRAINTS is a hexadecimal representation of the general_constraint_indicator_flags. 
> +                 * each byte is separated by a '.', and trailing zero bytes may be omitted.
> +                 * drop the trailing zero bytes refer to ISO/IEC14496-15.
> +                 */
> +                high_nibble = rbsp_buf[7] >> 4;
> +                snprintf(constraints, sizeof(constraints),
> +                         high_nibble ? "%02x.%x" : "%02x",
> +                         rbsp_buf[6], high_nibble);
>                 /* skip 8 + 8 + 32 + 4 + 43 + 1 bit */
>                 level = rbsp_buf[12];
>                 av_freep(&rbsp_buf);
> @@ -417,8 +445,11 @@ static void write_codec_attr(AVStream *st, VariantStream *vs)
>         }
>         if (st->codecpar->codec_tag == MKTAG('h','v','c','1') &&
>             profile != AV_PROFILE_UNKNOWN &&
> -            level != AV_LEVEL_UNKNOWN) {
> -            snprintf(attr, sizeof(attr), "%s.%d.4.L%d.B01", av_fourcc2str(st->codecpar->codec_tag), profile, level);
> +            profile_compatibility != AV_PROFILE_UNKNOWN &&
> +            tier != '0' &&
> +            level != AV_LEVEL_UNKNOWN &&
> +            strcmp(constraints, "0") != 0) {
> +            snprintf(attr, sizeof(attr), "%s.%d.%x.%c%d.%s", av_fourcc2str(st->codecpar->codec_tag), profile, profile_compatibility, tier, level, constraints);
>         } else
>             goto fail;
>     } else if (st->codecpar->codec_id == AV_CODEC_ID_MP2) {
> -- 
> 2.47.1
> 
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Thanks for your reply!
I already submit new patch, there are some changes in new patch:

1. Avoid using loop traversal, 
2. optimize constraint default value processing, 
3. and simplify the reading method of profile_compatibility_flags

BTW, I think the constraints[8] = “” maybe better, it can be check if the first bit is ‘\0’ so that maybe faster?

Regards
Jack