[FFmpeg-user] H264 VAAPI Encoder

Mark Thompson sw at jkqxz.net
Sat May 14 18:41:17 CEST 2016

On 13/05/16 20:43, Armin K. wrote:
> I noticed that recently a VAAPI based H264 encoder was added to ffmpeg.
> I built ffmpeg from git and now I have h264_vaapi listed in ffmpeg -encoders
> output.
> However, when I try to use ffmpeg ... -vcodec h264_vaapi I get the following
> error:
> Impossible to convert between the formats supported by the filter 'Parsed_null_0' and the filter 'auto-inserted scaler 0'
> The command I use is:
> ffmpeg -hwaccel vaapi -i <inputfile> -vcodec h264_vaapi <outfile>.mkv

Short answer:

ffmpeg -vaapi_device /dev/dri/renderD128 -i <inputfile> -vf 'format=nv12,hwupload' -c:v h264_vaapi <outfile>.mkv

Longer answer:

It's somewhat awkward to use because it only accepts input as VAAPI surfaces (AV_PIX_FMT_VAAPI), with underlying format depending on the particular hardware.

"-vaapi_device" sets the hardware device to use.  It takes either a DRI device (ideally a render node, as above) or an X11 display name (only if you are actually in X).

Then we use libavfilter to get the input into the right form:

"format=nv12" forces software conversion to NV12, which is the underlying format required by the Intel driver.

"hwupload" uploads that software image into a VAAPI surface, which can then be fed into the encoder.

You need a bit more trickiness to do a pure hardware transcode, see <https://wiki.libav.org/Hardware/vaapi> for additional explanation.

- Mark

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