[FFmpeg-devel] [PATCH] gifdec: resync support

[Paul B Mahol]

On 1/21/13, Michael Niedermayer <michaelni at gmx.at> wrote:
> This allows decoding gifs that have junk at the begin
> and also allows byte wise seeking
>
> Signed-off-by: Michael Niedermayer <michaelni at gmx.at>
> ---
>  libavformat/gifdec.c |   32 ++++++++++++++++++++++++++------
>  1 file changed, 26 insertions(+), 6 deletions(-)
>
> diff --git a/libavformat/gifdec.c b/libavformat/gifdec.c
> index 4f4ce2c..357d698 100644
> --- a/libavformat/gifdec.c
> +++ b/libavformat/gifdec.c
> @@ -70,6 +70,19 @@ static int gif_probe(AVProbeData *p)
>      return AVPROBE_SCORE_MAX;
>  }
>
> +static int resync(AVIOContext *pb)
> +{
> +    int i;
> +    for (i=0; i<6; i++) {

for (i = 0; i < 6; i++) {

> +        int b = avio_r8(pb);
> +        if(b != gif87a_sig[i] && b != gif89a_sig[i])

' ' after if

> +            i = -(b != 'G');
> +        if(url_feof(pb))

ditto

> +            return AVERROR_EOF;
> +    }
> +    return 0;
> +}
> +
>  static int gif_read_header(AVFormatContext *s)
>  {
>      GIFDemuxContext *gdc = s->priv_data;
> @@ -77,8 +90,7 @@ static int gif_read_header(AVFormatContext *s)
>      AVStream        *st;
>      int width, height, ret;
>
> -    /* skip 6-byte magick */
> -    if ((ret = avio_skip(pb, 6)) < 0)
> +    if ((ret = resync(pb)) < 0)
>          return ret;
>
>      gdc->delay  = gdc->default_delay;
> @@ -171,6 +183,7 @@ static int gif_read_packet(AVFormatContext *s, AVPacket
> *pkt)
>      }
>
>      if (keyframe) {
> +parse_keyframe:
>          /* skip 2 bytes of width and 2 of height */
>          if ((ret = avio_skip(pb, 4)) < 0)
>              return ret;
> @@ -196,7 +209,7 @@ static int gif_read_packet(AVFormatContext *s, AVPacket
> *pkt)
>      while (GIF_TRAILER != (block_label = avio_r8(pb)) && !url_feof(pb)) {
>          if (block_label == GIF_EXTENSION_INTRODUCER) {
>              if ((ret = gif_read_ext (s)) < 0 )
> -                return ret;
> +                goto resync;
>          } else if (block_label == GIF_IMAGE_SEPARATOR) {
>              /* skip to last byte of Image Descriptor header */
>              if ((ret = avio_skip(pb, 8)) < 0)
> @@ -215,11 +228,11 @@ static int gif_read_packet(AVFormatContext *s,
> AVPacket *pkt)
>              /* read LZW Minimum Code Size */
>              if (avio_r8(pb) < 1) {
>                  av_log(s, AV_LOG_ERROR, "lzw minimum code size must be >=
> 1\n");
> -                return AVERROR_INVALIDDATA;
> +                goto resync;
>              }
>
>              if ((ret = gif_skip_subblocks(pb)) < 0)
> -                return ret;
> +                goto resync;
>
>              frame_end = avio_tell(pb);
>
> @@ -244,7 +257,14 @@ static int gif_read_packet(AVFormatContext *s, AVPacket
> *pkt)
>              break;
>          } else {
>              av_log(s, AV_LOG_ERROR, "invalid block label\n");
> -            return AVERROR_INVALIDDATA;
> +resync:
> +            if (!keyframe)
> +                avio_seek(pb, frame_start, SEEK_SET);
> +            if((ret = resync(pb)) < 0)

' ' after if.

> +                return ret;
> +            frame_start = avio_tell(pb) - 6;
> +            keyframe = 1;
> +            goto parse_keyframe;
>          }
>      }
>
> --
> 1.7.9.5

lgtm, but please follow current style.