[FFmpeg-devel] [PATCH 3/4] lavf/mp3enc: write encoder delay/padding upon closing

[James Almer]

On 9/26/2016 2:13 PM, Jon Toohill wrote:
> trailing_padding is not known before encoding.
> ---
>  libavformat/mp3enc.c | 20 +++++++++++++-------
>  1 file changed, 13 insertions(+), 7 deletions(-)
> 
> diff --git a/libavformat/mp3enc.c b/libavformat/mp3enc.c
> index de63401..433b070 100644
> --- a/libavformat/mp3enc.c
> +++ b/libavformat/mp3enc.c
> @@ -247,12 +247,7 @@ static int mp3_write_xing(AVFormatContext *s)
>      ffio_fill(dyn_ctx, 0, 8); // empty replaygain fields
>      avio_w8(dyn_ctx, 0);      // unknown encoding flags
>      avio_w8(dyn_ctx, 0);      // unknown abr/minimal bitrate
> -
> -    // encoder delay
> -    if (par->initial_padding - 528 - 1 >= 1 << 12) {
> -        av_log(s, AV_LOG_WARNING, "Too many samples of initial padding.\n");
> -    }
> -    avio_wb24(dyn_ctx, FFMAX(par->initial_padding - 528 - 1, 0)<<12);
> +    avio_wb24(dyn_ctx, 0);    // empty encoder delay/padding
>  
>      avio_w8(dyn_ctx,   0); // misc
>      avio_w8(dyn_ctx,   0); // mp3gain
> @@ -381,7 +376,7 @@ static void mp3_update_xing(AVFormatContext *s)
>      AVReplayGain *rg;
>      uint16_t tag_crc;
>      uint8_t *toc;
> -    int i, rg_size;
> +    int i, rg_size, delay, padding;
>  
>      /* replace "Xing" identification string with "Info" for CBR files. */
>      if (!mp3->has_variable_bitrate)
> @@ -422,6 +417,17 @@ static void mp3_update_xing(AVFormatContext *s)
>          }
>      }
>  
> +    /* write encoder delay/padding */
> +    delay = FFMAX(s->streams[0]->codec->initial_padding - 528 - 1, 0);
> +    padding = s->streams[0]->codec->trailing_padding;

codecpar.

> +    if (delay >= 1 << 12) {
> +        av_log(s, AV_LOG_WARNING, "Too many samples of initial padding.\n");
> +    }
> +    if (padding >= 1 << 12) {
> +        av_log(s, AV_LOG_WARNING, "Too many samples of initial padding.\n");
> +    }
> +    AV_WB24(mp3->xing_frame + mp3->xing_offset + 141, (delay << 12) + padding);
> +
>      AV_WB32(mp3->xing_frame + mp3->xing_offset + XING_SIZE - 8, mp3->audio_size);
>      AV_WB16(mp3->xing_frame + mp3->xing_offset + XING_SIZE - 4, mp3->audio_crc);
>  
>