[libav-api] H.264 decoder using libavcodec

Prashanth Bhat prashanth_b_bhat at yahoo.com
Tue Aug 5 12:10:36 CEST 2014


Hi,

I'm using libavcodec to perform decoding of H.264 frames. 

I'm on a Linux environment (14.04 Xubuntu), and Intel Haswell CPU.

My program decodes the frames, without rendering them on the screen. With 4 simultaneous decodes of 1080p resolution and 15 fps, the CPU utilization is around 90% (not bad), but the load average shown by 'top' is 20+

This looks excessive. I don't think I'm using the hardware decoding ability of the Haswell CPU. Could someone please advise how to find out if I'm effectively using the decoder?

The API calls I'm making are pretty standard - 
avcodec_register_all();

avcodec_alloc_context3(NULL);

avcodec_find_decoder(AV_CODEC_ID_H264);

av_parser_init(AV_CODEC_ID_H264);

avcodec_open2();


The above calls are made during initialization. The below calls are made on each frame -

av_parser_parse2

avcodec_decode_video2


The following points are probably relevant - 
a) The default context allocated by avcodec_alloc_context3() does not have any hw_accel associated with it. I allocated a h264_vaapi accelerator, but this doesn't lead to any improvement.
b) The codec capabilities does not have the HW_ACCEL bit set.

Any help would be appreciated. 

Thanks,
Prashanth


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