[FFmpeg-devel] [PATCH] avformat/mov: parse the last moof box when mp4 segment format

[wangyaqiang]

ping

> 2022年9月1日 18:22，1035567130 at qq.com 写道：
> 
> From: Wang Yaqiang <wangyaqiang03 at kuaishou.com>
> 
> In the format of mp4 segment, the bitrate calculation of
> stream depends on the sample_size in moof->traf->trun box.
> In the original logic, when the last sidx box is read,
> it is not parsed backwards, and the total sample_size calculation is smaller.
> As a result, the bitrate displayed by ffprobe is also smaller than the actual.
> Increasing the moof_count variable ensures that the last moof is parsed.
> 
> Test method: You can use -c copy remux a fmp4 file as mp4
> and ffprobe the two files will find that the bitrate is inconsistent
> Befor patch:
> Stream #0:1[0x2](und): Audio: aac (HE-AAC) (mp4a / 0x6134706D), 44100 Hz, stereo, fltp, 59 kb/s
> After patch:
> Stream #0:1[0x2](und): Audio: aac (HE-AAC) (mp4a / 0x6134706D), 44100 Hz, stereo, fltp, 96 kb/s (default)
> 
> Signed-off-by: Wang Yaqiang <wangyaqiang03 at kuaishou.com>
> ---
> libavformat/isom.h | 1 +
> libavformat/mov.c  | 8 +++++++-
> 2 files changed, 8 insertions(+), 1 deletion(-)
> 
> diff --git a/libavformat/isom.h b/libavformat/isom.h
> index f05c2d9c28..183a3c486b 100644
> --- a/libavformat/isom.h
> +++ b/libavformat/isom.h
> @@ -296,6 +296,7 @@ typedef struct MOVContext {
>     int has_looked_for_mfra;
>     int use_tfdt;
>     MOVFragmentIndex frag_index;
> +    int moof_count; //ensure last fragment parse moof box
>     int atom_depth;
>     unsigned int aax_mode;  ///< 'aax' file has been detected
>     uint8_t file_key[20];
> diff --git a/libavformat/mov.c b/libavformat/mov.c
> index 14550e6456..396658e342 100644
> --- a/libavformat/mov.c
> +++ b/libavformat/mov.c
> @@ -7784,12 +7784,15 @@ static int mov_read_default(MOVContext *c, AVIOContext *pb, MOVAtom atom)
>             int64_t start_pos = avio_tell(pb);
>             int64_t left;
>             int err = parse(c, pb, a);
> +            if (a.type == MKTAG('m','o','o','f')) {
> +                c->moof_count ++;
> +            }
>             if (err < 0) {
>                 c->atom_depth --;
>                 return err;
>             }
>             if (c->found_moov && c->found_mdat && a.size <= INT64_MAX - start_pos &&
> -                ((!(pb->seekable & AVIO_SEEKABLE_NORMAL) || c->fc->flags & AVFMT_FLAG_IGNIDX || c->frag_index.complete) ||
> +                ((!(pb->seekable & AVIO_SEEKABLE_NORMAL) || c->fc->flags & AVFMT_FLAG_IGNIDX || (c->frag_index.complete && c->moof_count >= c->frag_index.nb_items)) ||
>                  start_pos + a.size == avio_size(pb))) {
>                 if (!(pb->seekable & AVIO_SEEKABLE_NORMAL) || c->fc->flags & AVFMT_FLAG_IGNIDX || c->frag_index.complete)
>                     c->next_root_atom = start_pos + a.size;
> @@ -8361,6 +8364,9 @@ static int mov_read_header(AVFormatContext *s)
>         av_log(s, AV_LOG_ERROR, "moov atom not found\n");
>         return AVERROR_INVALIDDATA;
>     }
> +    if (mov->frag_index.nb_items > mov->moof_count) {
> +        av_log(s, AV_LOG_WARNING, "the number of moof is less then fragment count\n");
> +    }
>     av_log(mov->fc, AV_LOG_TRACE, "on_parse_exit_offset=%"PRId64"\n", avio_tell(pb));
> 
>     if (pb->seekable & AVIO_SEEKABLE_NORMAL) {
> -- 
> 2.33.0
>