FFMPEG usage guide

Hardware (VAAPI) accelerated video format conversion

Conversion

Using FFMPEG CLI for converting videos

Example command

ffmpeg \
    -hwaccel vaapi -vaapi_device /dev/dri/renderD128
    -i input.mp4 \
    -vf 'format=nv12,hwupload,scale_vaapi=w=2560:h=1440' \
    -c:v h264_vaapi \
    -q:v 21 \
    output.mp4

This asks ffmpeg

• -hwaccel vaapi : to use vaapi hardware accel device

• -vaapi_device DEVICE : where to find the device

• format=nv12 : to first format as nv12

• hwupload : to upload to GPU

  VAAPI understands nv12, and hence the conversion beforehand

• scale_vaapi=DIMENSIONS : tells ffmpeg to scale the VAAPI buffer

• -c:v h264_vaapi : asks ffmpeg to encode the output using h264_vaapi in GPU

  Use -c:v libx264 for slower, but better quality encoding in CPU

• -q:v 21 : sets the video Quality Param to 21

  See Quality Param section below

Quality Param

With VAAPI

• QP 18–22: good quality
• QP 24–30: visible artifacts
• QP 12–16: very high quality / large files

Changing container formats

FFMPEG can be used to change container formats (.mp4, .mkv, .webm)

Example command

ffmpeg \
    -i input.mp4 \
    -c:v copy \
    -c:a copy \
    output.mkv

This asks ffmpeg

• c:v copy : copy the video stream without decoding
• c:a copy : copy the audio stream without decoding

This might cause issue when for example trying to copy an Opus audio stream into a .mp4 container. MP4 won't accept that, in which case you'd have to use another codec to encode the Opus stream to another format

Changing audio format

ffmpeg \
    -i input.mp4 \
    -c:v copy \
    -c:a aac -b:a 192k \
    output.mp4

This asks ffmpeg

• -c:a aac : encode to aac format
• -b:a 192k : use 192khz bit-rate for the audio