[FFmpeg-user] ffmpeg qsv performance well below expected

dan dandenson at gmail.com
Sat Jan 2 02:12:07 EET 2021

In running ubuntu with an i3-10100

I'm able to transcode 2 MPEG2 to h.265 using the following command
ffmpeg -hwaccel qsv -i http://hdhomerun:5004/auto/v2.2.ts -c:v
hevc_qsv -c:a copy -profile:v main -global_quality 30 -g 48
-keyint_min 48 -sc_threshold 0 -hls_time 2 -hls_list_size 10
-hls_segment_type mpegts -hls_flags delete_segments
-hls_segment_filename video_%03d.ts video.m3u8

but, the third video causes all 3 to start to throw errors in
encoding.  CPU usage on this quad core CPU is about 35% on 3 different
cores, seems there's no issue with CPU (general purpose) performance.
Am I hitting a wall on hevc_qsv here?

I've switched -hwaccel to vaapi which works but performance is a bit
worse.  I've removed this to push the MPEG2 decode to software, no
real effect.

I've tried to start the 3rd encode with libx265 but that crushes the CPU.

h264_qsv is able to handle this.

It appears, at least on the surface, that this CPU w/ 28 video cores
can only handle 2 h.265 encodes in quicksync but the specs seem to
suggest it should do more.

Am I missing something obvious?

note, the first 2 streams are 1080i MPEG2 from an HDHomeRun.  The
third stream I selected a 720p MPEG2 stream and even that doesn't work
well.  Also, I am not using any deinterlacer, I removed them to try to
get the third stream running.

Thanks for any feedback.

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