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• As part of my program that I am writing I am using ffmpeg. I am debugging. Why would ffmpeg run slower on a GPU than a CPU when doing mp4 compression ? [closed]

  6 mai 2023, par user875234

  I'm running it on modern equipment with latest drivers. I use it to compress video files, like so :

  


  ffmpeg -i 20230502_200913.mp4 -vcodec libx265 -crf 28 -vf "scale=trunc(iw/10)*2:trunc(ih/10)*2" output.mp4


  


  that command runs in 160 seconds on the CPU. but if I use the GPU, like so :

  


  ffmpeg -hwaccel cuda -i 20230502_200913.mp4 -vcodec libx265 -crf 28 -vf "scale=trunc(iw/10)*2:trunc(ih/10)*2" output.mp4


  


  it actually takes 280 seconds. And again, these are same era CPU and GPU. I can see it uses 100% of the GPU when running on the GPU but only 50% of the CPU when running on the CPU. I expected it to run much faster on the GPU than the CPU.

  


  Am I missing something ?

  


• Player downloads all moof part of a fragment mp4 file before playing

  28 mars 2023, par happyz90

  I converted a mp4 to fragment mp4 with the following command :

  


  ffmpeg -i ./input.mp4 -y -b:a 32k -vcodec libx265 -b:v 320k -bufsize 320k -tag:v hvc1 -color_primaries bt709 -color_trc bt709 -colorspace bt709 -c:a libfdk_aac -profile:a aac_he_v2 -movflags faststart+frag_keyframe+empty_moov+dash+global_sidx -chunk_duration 500000000 -max_muxing_queue_size 1024 ./output.mp4


  


  But when playing, the player send many http requests to download all the moof part :

  


  

  


  

  


  But I think in normal case the player only need to download the head part of the video file to play.

  


  So is there anything wrong with my ffmpeg parameters ? Please help me. Thank you.

  


• FFMPEG - modify only part of video with select filter

  28 janvier 2023, par Compact

  I have a video file - an NTSC DVD rip. I want to convert it into PAL DVD. The problem with that NTSC DVD is that it's a mixture of telecined content, true progressive 29.97 content, true interlaced content at 29.97 fps. The problem is with the true interlaced content - it's sometimes encoded as top field first and sometimes as bottom field first...

  


  To keep quality as much as possible, I would like remove telecined frames, but keep those interlaced sequences and turn them to 25 fps top field first. This is where the problem arises.

  


  I tried to make filter_complex chain with two select filters, where I reverse the fields for bottom field first frames, but the video is not encoding at all when I do that.

  


  Here is an example filter chain I tried to make - I've made a lot of iterations of something similar, using select or metadata select to no avail. I guess I don't understand how select and metadata select filters work. And I don't know how to do what I want.

  


  ffmpeg -i "input" -flags +ildct+ilme \
-filter_complex\
[0:v]idet,setparams=color_primaries=smpte170m:color_trc=bt709:colorspace=smpte170m \
,metadata=select:key=lavfi.idet.single.current_frame:value=bff:function=same_str,phase=b[bot];\[bot]metadata=select:key=lavfi.idet.single.current_frame:value=tff:function=same_str\
,fieldmatch=mode=pcn_ub:combmatch=full,decimate[tff];\
[tff]metadata=select:key=lavfi.idet.single.current_frame:value=progressive:function=same_str\
,fps=24000/1001[v1];[v1]select,setfield=tff[v]"


  


  If all of the interlaced content was top field first, I could simply do something similar to this :

  


  ffmpeg -i "input" -flags +ildct+ilme \
-filter:v "dejudder,fps=30000/1001,fieldmatch=mode=pcn_ub:combmatch=full,\
decimate,settb=1/25000,setpts=N/(25*TB),setfield=tff,setparams=field_mode=tff"


  


  Is that possible with ffmpeg ? To just modify a part of video and then modify it whole, including with the previous modification ?