[FFmpeg-devel] ffmpeg stuck in transcoding H264 using QSV

Chao Liu yijinliu at gmail.com
Tue Jul 26 09:04:49 EEST 2016


(Ivan, I am sending this mail to you directly because you said you are the
maintainer of QSV related code in a recent mail. Apologize if this is
inappropriate.. )

I am trying to use h264_qsv to transcode a MP4 file. This is my command:
ffmpeg -c:v h264_qsv -i input.mp4 -look_ahead 0 -c:v h264_qsv -b:v 800k
-maxrate 1600k -preset fast output.mp4
It always stucks in this loop

It works if I change the command to
ffmpeg -i input.mp4 -look_ahead 0 -c:v h264_qsv -b:v 800k -maxrate 1600k
-preset fast output.mp4
(not using qsv for decoding).

Looks like the decoding and encoding were contending for the resources and
there is a deadlock or sth. like that..

I tried to debug it a bit by comparing ffmpeg code with intel media SDK.
There is sth. I don't understand. Not sure whether it's related..
In ffmpeg, we decode the frame in a loop
<https://github.com/FFmpeg/FFmpeg/blob/master/libavcodec/qsvdec.c#L357>, it
sleeps and retries as long as MFXVideoDECODE_DecodeFrameAsync returns busy.
In intel media SDK sample_decode, it calls SyncOperation when
MFXVideoDECODE_DecodeFrameAsync returns busy.

Could this be the cause?

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