[Libav-user] MP4 files and avio_seek()

Williams, Blake bwilliams at drs.com
Wed May 18 23:22:59 CEST 2016

I'm trying to seek to a byte offset in an MP4 file.  I can't use avformat_seek_file() because the AVFMT_NO_BYTE_SEEK flag is set in the demuxer.

I'm reading the first 150 frames in the file, then seeking to a known file location.  I've been able to use avio_seek to set the m_pFormatCtx->pb->pos value to the correct offset, but the next call to av_read_frame() puts it right back to where it was, such that the next frame read is #151.  The seek code is:

                     int64_t filePos = m_posData.GetFrameOffset(frameNum);
                     int64_t ret = avio_seek(m_pFormatCtx->pb, filePos, SEEK_SET);

Is there something else that needs to be called to actually clear up the internal buffers so that av_read_frame will start at the correct location?


Blake Williams
Principal Software Engineer, Training and Control Systems
DRS Technologies, Inc.


645 Anchors Street
Fort Walton Beach, Florida 32548
Tel: 850.302-3281
 bwilliams at drs.com<mailto:CKuypers at DRS-DS.com>  || www.drs.com<http://www.drs.com/>

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