While reading the Linux Magazine on the bowl this morning, I discovered that ffmpeg has hardware support for decoding and encoding. Since I do that quite often, I figured it’s time to try it out. Lo and behold, it works better than I expected! Not on hadante, though. ffmpeg just segfaulted, because the card is way too old and the kernel module doesn’t seem to support it.
On othalla (my almost 4 year old laptop), it works like a charm. ffmpeg said encoding at 5.5 times the original speed, even over NFS!
The command line I used:
$Â ffmpeg -hwaccel cuvid -c:v h264_cuvid -resize 1280x720\ -i in.mkv -acodec copy -scodec copy\ -c:v h264_nvenc -preset slow -b:v 4000K -minrate 4000K out.mkv
It has a NVIDIA GPU, as well as an Intel pixel manager, but cuvid and nvenc only works the (proprietary) NVIDIA driver. Anyhow, as always it’s important where you place the options. Any options before -i is for decoding, anything after is for encoding. This makes:
-hwaccel cuvid -c:v h264_cuvid -resize 1280x720
ffmpeg decode everything via cuvid on the GPU and resize it to 720p. Source was 1080p.
-acodec copy -scodec copy
says: Just copy the audio stream and the subtitle stream to output. Now comes the important:
-c:v h264_nvenc -preset slow -b:v 4000K -minrate 4000K
tells it to let the GPU encode it to x264, preset slow and a minimum bitrate of 4000K. If I do the same via software decoder and encoder, I get barely more than real time speed, perhaps 1.1 or 1.2, depending on the source. With cuvid I get 5.5. Even Hadante with its 12 processors and 32GB only gets a speed of 2.0 to 2.2 max, and it’s hardware is much more current! Like it!