On Tue, 1 Sep 2015 11:35:17 -0700 Tsung-Hung Wu <tsungh...@chromium.org> wrote:
> Hi FFmpeg developers, > > I am trying to solve an issue: seeking a large MP3 file is slow. This > happens when play Podcast audio, for example > http://podcastdownload.npr.org/anon.npr-podcasts/podcast/344098539/430765119/npr_430765119.mp3 > It works not so good in less computing power mobile devices, especially > under slow network environment. > My goal is to improve the usability, although it may sacrifice the accuracy. > > I noticed that FFmpeg has AVFMT_FLAG_FAST_SEEK flag. That's exactly what I > need, sacrifices the accuracy of playback time in exchange for > responsiveness. However, it does not work as my expectation. I made some > changes to fulfill my needs. Please find the attachment for the patch. > Just to be clear, I put some comments below for discussions, which are not > in the patch. > > Could you please kindly review the attached patch? Let me know if you have > any comments. Thank you so much for your help. > > Best Regards, > Andy > > --- > libavformat/mp3dec.c | 14 ++++++++------ > 1 file changed, 8 insertions(+), 6 deletions(-) > > diff --git a/libavformat/mp3dec.c b/libavformat/mp3dec.c > index 007c6ea..7f675ab 100644 > --- a/libavformat/mp3dec.c > +++ b/libavformat/mp3dec.c > @@ -342,7 +342,7 @@ static int mp3_read_header(AVFormatContext *s) > int i; > > if (mp3->usetoc < 0) > - mp3->usetoc = (s->flags & AVFMT_FLAG_FAST_SEEK) ? 0 : 2; > + mp3->usetoc = (s->flags & AVFMT_FLAG_FAST_SEEK) ? 1 : 2; ok. > > /* > Should usetoc be 0 when AVFMT_FLAG_FAST_SEEK is enabled? When usetoc is 0, > seeking a VBR mp3 is slow, even if it contains a TOC. > Thus, I think 1 is a more proper selection. > */ > > st = avformat_new_stream(s, NULL); > if (!st) > @@ -489,19 +489,21 @@ static int mp3_seek(AVFormatContext *s, int > stream_index, int64_t timestamp, > AVStream *st = s->streams[0]; > int64_t ret = av_index_search_timestamp(st, timestamp, flags); > int64_t best_pos; > + int fast_seek = (s->flags & AVFMT_FLAG_FAST_SEEK) ? 1 : 0; > + int64_t filesize = mp3->header_filesize > 0 ? mp3->header_filesize > + : avio_size(s->pb) - s->internal->data_offset; ok. But maybe the avio_size() return value should be checked. It can return an error. > > /* > Many MP3 files in Podcast does not have VBRI, LAME, or XING tag, so > header_filesize is not always available. (file size - data offset) could be > a good estimation. > */ > > > if (mp3->usetoc == 2) > return -1; // generic index code > > - if ( mp3->is_cbr > + if ( (mp3->is_cbr || fast_seek) Not sure why you need this. If the file is VBR and has no TOC, then all odds are off. But I guess this is ok on the AVFMT_FLAG_FAST_SEEK code path, if you think it's more useful this way. > && (mp3->usetoc == 0 || !mp3->xing_toc) > && st->duration > 0 > - && mp3->header_filesize > s->internal->data_offset > - && mp3->frames) { > + && filesize > 0) { > /* > Not sure why (mp3->header_filesize > s->internal->data_offset) has to be > true. What if a MP3 file contains a short audio and a large picture? > Again, mp3->frames is not always available. Do we really need it here? I > move the check to below. > */ I can't think of any reason either. Maybe the original intention of this code was actually to check whether header_size is a sane value at all? There are lots of weird corner cases, like incomplete or concatenated mp3 files. > ie = &ie1; > timestamp = av_clip64(timestamp, 0, st->duration); > ie->timestamp = timestamp; > - ie->pos = av_rescale(timestamp, mp3->header_filesize, > st->duration) + s->internal->data_offset; > + ie->pos = av_rescale(timestamp, filesize, st->duration) + > s->internal->data_offset; > } else if (mp3->xing_toc) { > if (ret < 0) > return ret; > @@ -515,7 +517,7 @@ static int mp3_seek(AVFormatContext *s, int > stream_index, int64_t timestamp, > if (best_pos < 0) > return best_pos; > > - if (mp3->is_cbr && ie == &ie1) { > + if (mp3->is_cbr && ie == &ie1 && mp3->frames) { Not sure what this does after all. > int frame_duration = av_rescale(st->duration, 1, mp3->frames); > ie1.timestamp = frame_duration * av_rescale(best_pos - > s->internal->data_offset, mp3->frames, mp3->header_filesize); > } _______________________________________________ ffmpeg-devel mailing list ffmpeg-devel@ffmpeg.org http://ffmpeg.org/mailman/listinfo/ffmpeg-devel
