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gifdec: resync support

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This allows decoding gifs that have junk at the begin
and also allows byte wise seeking

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
This commit is contained in:
Michael Niedermayer
2013-01-21 18:52:01 +01:00
parent 40b4468f62
commit 13aca070ab
1 changed files with 26 additions and 6 deletions
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32
libavformat/gifdec.c
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@@ -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++) {
int b = avio_r8(pb);
if (b != gif87a_sig[i] && b != gif89a_sig[i])
i = -(b != 'G');
if (url_feof(pb))
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)
return ret;
frame_start = avio_tell(pb) - 6;
keyframe = 1;
goto parse_keyframe;
}
}