Commit 2b3e9bbfb529e6bde238aeb511b55ebe461664c8 caused problems for a certain API user:
https://code.google.com/p/chromium/issues/detail?id=537725 https://code.google.com/p/chromium/issues/detail?id=542032 The problem seems rather arbitrary, because if there's junk, anything can happen. In this case, the imperfect junk skipping just caused it to read different junk, from what I can see. We can improve the accuracy of junk detection by a lot by checking if 2 consecutive frames use the same configuration. While in theory it might be completely fine for the 1st frame to have a different format than the 2nd frame, it's exceedingly unlikely, and I can't think of a legitimate use-case. This is approximately the same mpg123 does for junk skipping, and the set of compared header bits is exactly the same. --- The reason Chromium had so much problems with this is that they don't allow mid-stream format changes at all, and the junk triggered format changes. (Would be nice if Google paid me for this.) --- libavformat/mp3dec.c | 25 ++++++++++++++++++------- 1 file changed, 18 insertions(+), 7 deletions(-) diff --git a/libavformat/mp3dec.c b/libavformat/mp3dec.c index d3080d7..e7b6234 100644 --- a/libavformat/mp3dec.c +++ b/libavformat/mp3dec.c @@ -54,7 +54,7 @@ typedef struct { int is_cbr; } MP3DecContext; -static int check(AVIOContext *pb, int64_t pos); +static int check(AVIOContext *pb, int64_t pos, uint32_t *header); /* mp3 read */ @@ -374,12 +374,21 @@ static int mp3_read_header(AVFormatContext *s) off = avio_tell(s->pb); for (i = 0; i < 64 * 1024; i++) { + uint32_t header, header2; + int frame_size; if (!(i&1023)) ffio_ensure_seekback(s->pb, i + 1024 + 4); - if (check(s->pb, off + i) >= 0) { - av_log(s, AV_LOG_INFO, "Skipping %d bytes of junk at %"PRId64".\n", i, off); - avio_seek(s->pb, off + i, SEEK_SET); - break; + frame_size = check(s->pb, off + i, &header); + if (frame_size > 0) { + avio_seek(s->pb, off, SEEK_SET); + ffio_ensure_seekback(s->pb, i + 1024 + frame_size + 4); + if (check(s->pb, off + i + frame_size, &header2) >= 0 && + (header & 0xFFFEFCF0) == (header2 & 0xFFFEFCF0)) + { + av_log(s, AV_LOG_INFO, "Skipping %d bytes of junk at %"PRId64".\n", i, off); + avio_seek(s->pb, off + i, SEEK_SET); + break; + } } avio_seek(s->pb, off, SEEK_SET); } @@ -420,7 +429,7 @@ static int mp3_read_packet(AVFormatContext *s, AVPacket *pkt) #define SEEK_WINDOW 4096 -static int check(AVIOContext *pb, int64_t pos) +static int check(AVIOContext *pb, int64_t pos, uint32_t *ret_header) { int64_t ret = avio_seek(pb, pos, SEEK_SET); unsigned header; @@ -434,6 +443,8 @@ static int check(AVIOContext *pb, int64_t pos) if (avpriv_mpegaudio_decode_header(&sd, header) == 1) return -1; + if (ret_header) + *ret_header = header; return sd.frame_size; } @@ -461,7 +472,7 @@ static int64_t mp3_sync(AVFormatContext *s, int64_t target_pos, int flags) continue; for(j=0; j<MIN_VALID; j++) { - ret = check(s->pb, pos); + ret = check(s->pb, pos, NULL); if(ret < 0) break; if ((target_pos - pos)*dir <= 0 && abs(MIN_VALID/2-j) < score) { -- 2.5.1 _______________________________________________ ffmpeg-devel mailing list ffmpeg-devel@ffmpeg.org http://ffmpeg.org/mailman/listinfo/ffmpeg-devel
