[FFmpeg-devel] [PATCH 03/49] fftools/ffmpeg: stop using OutputStream.frame_number for streamcopy

[James Almer]

On 4/4/2022 8:29 AM, Anton Khirnov wrote:
> This field is currently used by checks
> - skipping packets before the first keyframe
> - skipping packets before start time
> to test whether any packets have been output already. But since
> frame_number is incremented after the bitstream filters are applied
> (which may involve delay), this use is incorrect. The keyframe check
> works around this by adding an extra flag, the start-time check does
> not.
> 
> Simplify both checks by replacing the seen_kf flag with a flag tracking
> whether any packets have been output by do_streamcopy().
> ---
>   fftools/ffmpeg.c | 10 +++++-----
>   fftools/ffmpeg.h |  2 +-
>   2 files changed, 6 insertions(+), 6 deletions(-)
> 
> diff --git a/fftools/ffmpeg.c b/fftools/ffmpeg.c
> index 13be32f0cf..29b01f9d93 100644
> --- a/fftools/ffmpeg.c
> +++ b/fftools/ffmpeg.c
> @@ -894,8 +894,6 @@ static void output_packet(OutputFile *of, AVPacket *pkt,
>   
>       /* apply the output bitstream filters */
>       if (ost->bsf_ctx) {
> -        if (pkt->flags & AV_PKT_FLAG_KEY)
> -            ost->seen_kf = 1;
>           ret = av_bsf_send_packet(ost->bsf_ctx, eof ? NULL : pkt);
>           if (ret < 0)
>               goto finish;
> @@ -2043,11 +2041,11 @@ static void do_streamcopy(InputStream *ist, OutputStream *ost, const AVPacket *p
>           return;
>       }
>   
> -    if ((!ost->frame_number && !(pkt->flags & AV_PKT_FLAG_KEY)) &&
> -        !ost->copy_initial_nonkeyframes && !ost->seen_kf)
> +    if (!ost->streamcopy_started && !(pkt->flags & AV_PKT_FLAG_KEY) &&
> +        !ost->copy_initial_nonkeyframes)
>           return;
>   
> -    if (!ost->frame_number && !ost->copy_prior_start) {
> +    if (!ost->streamcopy_started && !ost->copy_prior_start) {
>           int64_t comp_start = start_time;
>           if (copy_ts && f->start_time != AV_NOPTS_VALUE)
>               comp_start = FFMAX(start_time, f->start_time + f->ts_offset);
> @@ -2101,6 +2099,8 @@ static void do_streamcopy(InputStream *ist, OutputStream *ost, const AVPacket *p
>       ost->sync_opts += opkt->duration;
>   
>       output_packet(of, opkt, ost, 0);
> +
> +    ost->streamcopy_started = 1;
>   }
>   
>   int guess_input_channel_layout(InputStream *ist)
> diff --git a/fftools/ffmpeg.h b/fftools/ffmpeg.h
> index 1e14bf9fa9..04369df139 100644
> --- a/fftools/ffmpeg.h
> +++ b/fftools/ffmpeg.h
> @@ -536,7 +536,7 @@ typedef struct OutputStream {
>       int inputs_done;
>   
>       const char *attachment_filename;
> -    int seen_kf;
> +    int streamcopy_started;
>       int copy_initial_nonkeyframes;
>       int copy_prior_start;
>       char *disposition;

fate-ffmpeg-setts-bsf, which depends on this code, still passes, so lgtm.