[FFmpeg-devel] [PATCH] avformat/dashenc: add hevc codec attributes parse

[Zhao Zhili]

> On Mar 12, 2025, at 15:06, Jack Lau via ffmpeg-devel <ffmpeg-devel at ffmpeg.org> wrote:
> 
> fix ticket: 11316
> add set_hevc_codec_str function refer to hlsenc.c but do some necessary changes
> Signed-off-by: Jack Lau <jacklau1222 at qq.com>
> ---
> libavformat/dashenc.c | 81 +++++++++++++++++++++++++++++++++++++++++++
> 1 file changed, 81 insertions(+)
> 
> diff --git a/libavformat/dashenc.c b/libavformat/dashenc.c
> index d4a6fe0304..04c5b562d5 100644
> --- a/libavformat/dashenc.c
> +++ b/libavformat/dashenc.c
> @@ -57,6 +57,7 @@
> #include "url.h"
> #include "vpcc.h"
> #include "dash.h"
> +#include "nal.h"
> 
> typedef enum {
>     SEGMENT_TYPE_AUTO = 0,
> @@ -344,6 +345,84 @@ static void set_vp9_codec_str(AVFormatContext *s, AVCodecParameters *par,
>     return;
> }
> 
> +static void set_hevc_codec_str(AVCodecParameters *par, char *str, int size) {
> +    uint8_t *data = par->extradata;
> +    int profile = AV_PROFILE_UNKNOWN;
> +    uint32_t profile_compatibility = AV_PROFILE_UNKNOWN; 
> +    char tier = 0;
> +    int level = AV_LEVEL_UNKNOWN;
> +    char constraints[8] = "";
> +
> +    if (par->profile != AV_PROFILE_UNKNOWN)
> +        profile = par->profile;
> +    if (par->level != AV_LEVEL_UNKNOWN)
> +        level = par->level;
> +
> +    /* check the boundary of data which from current position is small than extradata_size */
> +    while (data && (data - par->extradata + 19) < par->extradata_size) {
> +        /* get HEVC SPS NAL and seek to profile_tier_level */
> +        if (!(data[0] | data[1] | data[2]) && data[3] == 1 && ((data[4] & 0x7E) == 0x42)) {
> +            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 */
> +            remain_size = par->extradata_size - (data - par->extradata);
> +            rbsp_buf = ff_nal_unit_extract_rbsp(data, remain_size, &rbsp_size, 0);
> +            if (!rbsp_buf)
> +                return;
> +            if (rbsp_size < 13) {
> +                av_freep(&rbsp_buf);
> +                break;
> +            }
> +            /* skip sps_video_parameter_set_id   u(4),
> +            *      sps_max_sub_layers_minus1    u(3),
> +            *  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 = (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 = AV_RB32(rbsp_buf + 2);
> +            /* revise these bits to get the profile compatibility value */
> +            profile_compatibility_flags = ((profile_compatibility_flags & 0x55555555U) << 1) | ((profile_compatibility_flags >> 1) & 0x55555555U);
> +            profile_compatibility_flags = ((profile_compatibility_flags & 0x33333333U) << 2) | ((profile_compatibility_flags >> 2) & 0x33333333U);
> +            profile_compatibility_flags = ((profile_compatibility_flags & 0x0F0F0F0FU) << 4) | ((profile_compatibility_flags >> 4) & 0x0F0F0F0FU);
> +            profile_compatibility_flags = ((profile_compatibility_flags & 0x00FF00FFU) << 8) | ((profile_compatibility_flags >> 8) & 0x00FF00FFU);
> +            profile_compatibility = (profile_compatibility_flags << 16) | (profile_compatibility_flags >> 16);
> +            /* 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);
> +            break;
> +        }
> +        data++;
> +    }
> +    if (profile != AV_PROFILE_UNKNOWN &&
> +        profile_compatibility != AV_PROFILE_UNKNOWN &&
> +        tier != 0 &&
> +        level != AV_LEVEL_UNKNOWN &&
> +        constraints[0] != '\0') {
> +        av_strlcatf(str, size, ".%d.%x.%c%d.%s", profile, profile_compatibility, tier, level, constraints);
> +    }
> +    return;
> +}
> +
> static void set_codec_str(AVFormatContext *s, AVCodecParameters *par,
>                           AVRational *frame_rate, char *str, int size)
> {
> @@ -422,6 +501,8 @@ static void set_codec_str(AVFormatContext *s, AVCodecParameters *par,
>             av_strlcatf(str, size, ".%02x%02x%02x",
>                         extradata[1], extradata[2], extradata[3]);
>         av_free(tmpbuf);
> +    } else if (!strcmp(str, "hev1") || !strcmp(str, "hvc1")) {
> +        set_hevc_codec_str(par, str, size);
>     } else if (!strcmp(str, "av01")) {
>         AV1SequenceParameters seq;
>         if (!par->extradata_size)

It’s not a good idea to copy-paste a lot of code between hls and dash.

> -- 
> 2.47.1
> 
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