[FFmpeg-user] Why is concat so slow on a powerful machine?

[Kevin Duffey]

Thanks. Sorry I should have included that info.
I have two files.. both are the same.. DNxHR SQ codec. Usually they are about 45mins each, sometimes different depending on if my battery died while filming! Sports games.
They reside on an SSD drive. I am on Windows 10 Home. I have a txt file set up demux.txt. The call I do is:
ffmpeg -f concat -safe 0 -i demux.txt -c copy output.movthe .mov is the container the DNxHR SQ files are in, and after letting it run for hours, the result worked. In that I got a DNxHR SQ file with the two files concatenated. 
This is the output I got when running it. Initially it started at 50fps, but quickly went to 15fps, then soon after .1fps. 

ffmpeg version 3.3.3 Copyright (c) 2000-2017 the FFmpeg developers  built with gcc 7.1.0 (GCC)  configuration: --enable-gpl --enable-version3 --enable-cuda --enable-cuvid --enable-d3d11va --enable-dxva2 --enable-libmfx --enable-nvenc --enable-avisynth --enable-bzlib --enable-fontconfig --enable-frei0r --enable-gnutls --enable-iconv --enable-libass --enable-libbluray --enable-libbs2b --enable-libcaca --enable-libfreetype --enable-libgme --enable-libgsm --enable-libilbc --enable-libmodplug --enable-libmp3lame --enable-libopencore-amrnb --enable-libopencore-amrwb --enable-libopenh264 --enable-libopenjpeg --enable-libopus --enable-librtmp --enable-libsnappy --enable-libsoxr --enable-libspeex --enable-libtheora --enable-libtwolame --enable-libvidstab --enable-libvo-amrwbenc --enable-libvorbis --enable-libvpx --enable-libwavpack --enable-libwebp --enable-libx264 --enable-libx265 --enable-libxavs --enable-libxvid --enable-libzimg --enable-lzma --enable-zlib  libavutil      55. 58.100 / 55. 58.100  libavcodec     57. 89.100 / 57. 89.100  libavformat    57. 71.100 / 57. 71.100  libavdevice    57.  6.100 / 57.  6.100  libavfilter     6. 82.100 /  6. 82.100  libswscale      4.  6.100 /  4.  6.100  libswresample   2.  7.100 /  2.  7.100  libpostproc    54.  5.100 / 54.  5.100[mov,mp4,m4a,3gp,3g2,mj2 @ 0000000000e6bb80] overread end of atom '⌐mak' by 2 bytes[mov,mp4,m4a,3gp,3g2,mj2 @ 0000000000e6bb80] overread end of atom '⌐swr' by 3 bytes[concat @ 0000000000e624a0] Could not find codec parameters for stream 1 (Unknown: none): unknown codecConsider increasing the value for the 'analyzeduration' and 'probesize' optionsInput #0, concat, from 'demux.txt':  Duration: N/A, start: 0.000000, bitrate: 461960 kb/s    Stream #0:0(eng): Video: dnxhd (DNXHR SQ) (AVdh / 0x68645641), yuv422p(tv, bt709, progressive), 3840x2160, 461960 kb/s, SAR 1:1 DAR 16:9, 23.98 fps, 23.98 tbr, 24k tbn, 24k tbc    Metadata:      creation_time   : 2024-10-10T23:17:36.000000Z      encoder         : Avid DNxHR Codec    Stream #0:1: Unknown: noneOutput #0, mov, to 'output.mov':  Metadata:    encoder         : Lavf57.71.100    Stream #0:0(eng): Video: dnxhd (DNXHR SQ) (AVdh / 0x68645641), yuv422p(tv, bt709, progressive), 3840x2160 [SAR 1:1 DAR 16:9], q=2-31, 461960 kb/s, 23.98 fps, 23.98 tbr, 24k tbn, 24k tbc    Metadata:      creation_time   : 2024-10-10T23:17:36.000000Z      encoder         : Avid DNxHR CodecStream mapping:  Stream #0:0 -> #0:0 (copy)Press [q] to stop, [?] for helpframe=   75 fps= 15 q=-1.0 size=  176400kB time=00:00:03.08 bitrate=468196.6kbits/s speed=0.621x
    On Wednesday, October 18, 2017, 1:16:40 AM PDT, Cley Faye <cleyfaye at gmail.com> wrote:  
 
 2017-10-18 3:17 GMT+02:00 Kevin Duffey <kevinmduffey-at-yahoo.com at ffmpeg.org
>:

> Yup. I do not specify the output. I just use the same .mov file extension
> as the two source files. Is it possible even though I specify -c copy
> out.mov it is rendering and not Concat??
>
>
>
​You really should provide a minimal command line reproducing the issue and
the output of ffmpeg, otherwise it will be impossible to divine what's
happening.

Or, if you want a general answer, no, concat should be fast assuming that
I/O are fast and the output muxer is fast. Without more information it is
hard to say anything more.​
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