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mp3: Make the seek more robust

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Try to parse up to 4 packets to find the closest packet.

Reported-By: jan.schlueter@ofai.at
This commit is contained in:
Luca Barbato 2015-07-11 17:38:26 +02:00
parent d80811c94e
commit c1d647b15a
1 changed files with 65 additions and 11 deletions
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76
libavformat/mp3dec.c
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@ -366,6 +366,67 @@ static int mp3_read_packet(AVFormatContext *s, AVPacket *pkt)
return ret;
}
#define SEEK_PACKETS 4
#define SEEK_WINDOW (SEEK_PACKETS * MP3_PACKET_SIZE)
/* The toc entry can position to the wrong byte offset, try to pick
* the closest frame by probing the data in a window of 4 packets.
*/
static int check(AVIOContext *pb, int64_t pos, int64_t *out_pos)
{
MPADecodeHeader mh = { 0 };
int i;
uint32_t header;
int64_t off = 0;
for (i = 0; i < SEEK_PACKETS; i++) {
off = avio_seek(pb, pos + mh.frame_size, SEEK_SET);
if (off < 0)
break;
header = avio_rb32(pb);
if (ff_mpa_check_header(header) < 0 ||
avpriv_mpegaudio_decode_header(&mh, header))
break;
out_pos[i] = off;
}
return i;
}
static int reposition(AVFormatContext *s, int64_t pos)
{
int ret, best_valid = -1;
int64_t p, best_pos = -1;
for (p = FFMAX(pos - SEEK_WINDOW / 2, 0); p < pos + SEEK_WINDOW / 2; p++) {
int64_t out_pos[SEEK_PACKETS];
ret = check(s->pb, p, out_pos);
if (best_valid < ret) {
int i;
for (i = 0; i < ret; i++) {
if (llabs(best_pos - pos) > llabs(out_pos[i] - pos)) {
best_pos = out_pos[i];
best_valid = ret;
}
}
if (best_pos == pos && best_valid == SEEK_PACKETS)
break;
}
}
if (best_valid <= 0)
return AVERROR(ENOSYS);
avio_seek(s->pb, best_pos, SEEK_SET);
return 0;
}
static int mp3_seek(AVFormatContext *s, int stream_index, int64_t timestamp,
int flags)
{
@ -373,7 +434,6 @@ static int mp3_seek(AVFormatContext *s, int stream_index, int64_t timestamp,
AVIndexEntry *ie;
AVStream *st = s->streams[0];
int64_t ret = av_index_search_timestamp(st, timestamp, flags);
uint32_t header = 0;
if (!mp3->xing_toc)
return AVERROR(ENOSYS);
@ -382,20 +442,14 @@ static int mp3_seek(AVFormatContext *s, int stream_index, int64_t timestamp,
return ret;
ie = &st->index_entries[ret];
ret = avio_seek(s->pb, ie->pos, SEEK_SET);
ret = reposition(s, ie->pos);
if (ret < 0)
return ret;
while (!s->pb->eof_reached) {
header = (header << 8) + avio_r8(s->pb);
if (ff_mpa_check_header(header) >= 0) {
ff_update_cur_dts(s, st, ie->timestamp);
ret = avio_seek(s->pb, -4, SEEK_CUR);
return (ret >= 0) ? 0 : ret;
}
}
ff_update_cur_dts(s, st, ie->timestamp);
return AVERROR_EOF;
return 0;
}
AVInputFormat ff_mp3_demuxer = {