Tomas Härdin <tjop...@acc.umu.se> 于2020年5月19日周二 下午10:25写道： > > fre 2020-05-15 klockan 10:14 +0800 skrev Tao Zhang: > > Marton Balint <c...@passwd.hu> 于2020年5月15日周五 上午2:33写道： > > > > > > > > > On Thu, 14 May 2020, Tao Zhang wrote: > > > > > > > Hi, > > > > FFmpeg supports multiple outputs created out of the same input in the > > > > same process like > > > > ffmpeg -i input -filter_complex '[0:v]yadif,split=3[out1][out2][out3]' \ > > > > -map '[out1]' -s 1280x720 -acodec … -vcodec … output1 \ > > > > -map '[out2]' -s 640x480 -acodec … -vcodec … output2 \ > > > > -map '[out3]' -s 320x240 -acodec … -vcodec … output3 > > > > In ffmpeg.c, multiple outputs are processed sequentially like > > > > for (i = 0; i < nb_output_streams; i++) > > > > encoding one frame; > > > > > > > > As below wiki noted, the slowest encoder will slow down the whole > > > > process. Some encoders (like libx264) perform their encoding "threaded > > > > and in the background", but x264_encoder_encode still cost some time. > > > > And it is noticeable when multiple x264_encoder_encodes run in the same > > > > thread. > > > > https://trac.ffmpeg.org/wiki/Creating%20multiple%20outputs > > > > > > > > For API users, they can use separate thread for multiple encoding in > > > > their own code. But is there any way to rescue command line users? > > > > > > I am not sure I understand what you want. Processing will still be limited > > > to the slowest encoder, because input processing will still be driven by > > > the slowest encoder, even if the encoders run in separate threads. > > > > > > Buffering encoder input frames is not an option, because input frames are > > > uncompressed, therefore huge. So if you want the faster x264 encoder to > > > finish faster, you have to drive it from a different input, ultimately you > > > should run 3 separate encode processes and accept that decoding and yadif > > > processing happens in all 3 cases separately causing some overhead. > > Currently FFmpeg works like below: > > main thread: > > encoding frame 1 for output 1; encoding frame 1 for output 2; encoding > > frame 1 for output 3; encoding frame 2 for output 1; encoding frame 2 > > for output 2; encoding frame 2 for output 3;... > > > > What I want to do is > > thread 1: > > encoding frame 1 for output 1; encoding frame 2 for output 1;... > > thread 2: > > encoding frame 1 for output 2; encoding frame 2 for output 2;... > > thread 3: > > encoding frame 1 for output 3; encoding frame 2 for output 3;... > > Why not just run multiple copies of the ffmpeg program? Decoding should > almost always be very minor work compared to encoding. Not vey minor IMHO. For same resolution, H264 decoding is about 10% computing cost of encoding. And if adding the filter computing cost (just as yadif filter listed above), the redundant computing cost is huge. _______________________________________________ ffmpeg-devel mailing list ffmpeg-devel@ffmpeg.org https://ffmpeg.org/mailman/listinfo/ffmpeg-devel
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