I apologize for the spam but I realized that this ML is mostly about patches. So I created a ticket here:
https://trac.ffmpeg.org/ticket/11137 Errata for the previous email: the seek timestamps should not be doubles but int64_t so the correct max_ts is 5120, not 0.5. On Mon, Aug 12, 2024 at 4:24 PM A <ahmadsha...@gmail.com> wrote: > Hi, > > My understanding is that avformat_seek_file() with these parameters: > > avformat_seek_file(format_context, 0, INT64_MIN, timestamp, timestamp) > > should seek in the video to an I-Frame that is strictly <= timestamp > (because ts=timestamp and max_ts=timestamp). > > However, the observed behavior that I see is that for certain H265 videos, > FFMPEG seeks beyond the timestamp passed in. To repro this behavior I ran > these commands: > > # Create a clean conda environment for testing purposes > conda create --name test > conda activate test > conda install -c conda-forge x265 > > # Install some build pre-requisites > conda install pkg-config > > # Build ffmpeg from source with x265 enabled > git clone https://github.com/FFmpeg/FFmpeg.git > ./configure --enable-nonfree --enable-gpl --prefix=$(readlink -f ../bin) > --enable-libx265 --enable-rpath > --extra-ldflags=-Wl,-rpath=$CONDA_PREFIX/lib --enable-filter=drawtext > --enable-libfontconfig --enable-libfreetype --enable-libharfbuzz > make -j install > > # Now generate a video with just frame numbers in the text per frame: > ffmpeg -f lavfi -i color=size=128x128:duration=1:rate=10:color=blue -vf > "drawtext=fontsize=30:fontcolor=white:x=(w-text_w)/2:y=(h-text_h)/2:text='Frame > %{frame_num}'" -vcodec libx265 -pix_fmt yuv420p -g 2 -crf 10 test.mp4 -y > > Note that this video has 10 frames. ffprobe shows the following: > > ffprobe -v error -select_streams v:0 -show_entries > frame=pts,pts_time,duration,pkt_pts_time,pkt_duration,key_frame -of csv > test.mp4 > frame,1,0,0.000000,1024,1024, > frame,0,1024,0.100000,1024,1024 > frame,1,2048,0.200000,1024,1024 > frame,0,3072,0.300000,1024,1024 > frame,1,4096,0.400000,1024,1024 > frame,0,5120,0.500000,1024,1024 > frame,1,6144,0.600000,1024,1024 > frame,0,7168,0.700000,1024,1024 > frame,1,8192,0.800000,1024,1024 > frame,0,9216,0.900000,1024,1024 > > Now, when I open this video using FFMPEG as a library, I get an > AVFormatContext. I want to decode the frame with pts=0.5. So I call > avformat_seek_file with min_ts=-INT64_MAX, ts=0.5 and max_ts=0.5. > > I expect that FFMPEG will seek to the frame with pts=0.4 so I can then > decode forward and eventually get frame with pts=0.5 with > avcodec_receive_frame(), but it seems like the first frame that I get from > avcodec_receive_frame() is the one with pts=0.6. > > More context: > I am writing a library that wraps FFMPEG and returns frames at arbitrary > timestamps. The full source code of the library is here: > https://github.com/pytorch/torchcodec. The pull-request that reproduces > this exact scenario is here: > https://github.com/pytorch/torchcodec/pull/178. > > It would be nice if FFMPEG always seeked to a frame with pts <= the > max_pts passed into avformat_seek_file. This normally does work with other > codecs. Am I calling the library wrong? Should I be calling > avformat_seek_file() with other flags? The documentation of > avformat_seek_file is here: > > > https://ffmpeg.org/doxygen/7.0/group__lavf__decoding.html#ga3b40fc8d2fda6992ae6ea2567d71ba30 > > Here is the seek call in my code: > > > https://github.com/pytorch/torchcodec/blob/dbfef1223522639d2b036a185b444eecf7748466/src/torchcodec/decoders/_core/VideoDecoder.cpp#L735 > > I would be happy to file a ticket as well, if that helps. The full repro > instructions are in this email for reference. > _______________________________________________ ffmpeg-devel mailing list ffmpeg-devel@ffmpeg.org https://ffmpeg.org/mailman/listinfo/ffmpeg-devel To unsubscribe, visit link above, or email ffmpeg-devel-requ...@ffmpeg.org with subject "unsubscribe".
