[FFmpeg-user] Ffmpeg Nvidia GPU mkv encoding output file size

oktay eşgül oktayesgul at gmail.com
Tue Apr 17 11:37:15 EEST 2018

I have  been working with below environment.

==>Ubuntu 16.04.3

==>FFmpeg :3.4.2

-- configuration: --prefix=/usr/local/ffmpeg_new/ --enable-cuda
--enable-cuvid --enable-nvenc --enable-nonfree --enable-libnpp
--extra-ldflags=-L/usr/local/cuda/lib64 --enable-libvpx --enable-libvorbis

==>Cuda 9.1.85

==> GPU: GeForce GTX 1080ti

==> I have two media files :

caller_video.webm (80MB) and callee_video.webm (120MB)

==> Then I am demuxing audios from these videos via below command:

time ffmpeg -y -i caller.webm -vn -ab 256 caller.wav

Caller.wav = 260 MB

==>Then, muxing caller.wav file with callee_video.webm

time ffmpeg -y -i callee_video.webm -i caller.wav -filter_complex

File Size of tempfile : 87MB

==>Then, I am encoding the temp file via below command:

time ffmpeg -y -i temp_file.mkv -pixel_format yuv444p -preset default -vf
drawtext=fontfile=/usr/share/fonts/truetype/dejavu/DejaVuSans-Bold.ttf:x=8:y=8:fontsize=16:fontcolor=yellow at 1:expansion=strftime:basetime=1518172680000000:text='%Y-%m-%d
%H-%M-%S' -acodec libvorbis -c:v h264_nvenc final_video.mkv

Final_video Size: 270 MB

==>The thing I am trying to understand is that when I encode the orig webm
file which is 80MB,the encoded output mkv file size ~20MB .

==>Yet, when I performed the same operation on muxed temp media
file(callee_video.webm + caller.wav) that the size is 87MB before encoding,
becomes 270MB .

Would you please share your comments what I am missing or doing wrong.

Thank you

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