[FFmpeg-devel] [PATCH 1/2] avdevice/decklink_dec: use a custom memory allocator

Dave Rice dave at dericed.com
Tue Jun 5 20:39:56 EEST 2018

> On Jun 5, 2018, at 1:17 PM, Marton Balint <cus at passwd.hu> wrote:
> On Tue, 5 Jun 2018, Dave Rice wrote:
>>> On Jun 4, 2018, at 4:21 PM, Marton Balint <cus at passwd.hu> wrote:
>>> The default memory allocator is limited in the max number of frames available,
>>> and therefore caused frame drops if the frames were not freed fast enough.
>> I’ve been testing this patchset today. Yesterday I was occasionally getting “Decklink input buffer overrun!” errors with this command:
>> /usr/local/opt/ffmpegdecklink/bin/ffmpeg-dl -v info -nostdin -nostats -t 1980 -f decklink -draw_bars 0 -audio_input embedded -video_input sdi -format_code ntsc -channels 8 -raw_format yuv422p10 -i "UltraStudio Express" -metadata:s:v:0 encoder="FFV1 version 3" -color_primaries smpte170m -color_trc bt709 -colorspace smpte170m -color_range mpeg -metadata creation_time=now -f_strict unofficial -c:v ffv1 -level 3 -g 1 -slices 16 -slicecrc 1 -c:a pcm_s24le -filter_complex "[0:v:0]setfield=bff,setsar=40/27,setdar=4/3; [0:a:0]pan=stereo| c0=c0 | c1=c1[stereo1];[0:a:0]pan=stereo| c0=c2 | c1=c3[stereo2]" -map "[stereo1]" -map "[stereo2]" -f matroska output.mkv -an -f framemd5 output.framemd5
>> With the patchset applied, I haven’t had that buffer overrun error re-occur.
> That is very strange, it should work the opposite way. Without the patch, the decklink driver is dropping frames (silently), so you should never get a Decklink input buffer overrun error message, but silent frame drops instead if you don't release (transcode) the frames fast enough.
> With the patch, you won't get silent frame drops, but you might fill the internal queue and therefore get Decklink input buffer overruns. On the other hand, if you get Decklink input buffer overruns, that typically means that your computer is too slow to handle transcoding in real time…

Trying to detect unreported dropped frames is why I added the framemd5 output as a second output. After the command runs, I would use this command

grep -v "^#” output.framemd5 | awk -F',' '$2!=p+1{printf p+1"-"$2-1" "}{p=$2}'

to report the ranges of pts that weren’t incrementing the pts by 1 within the pts. I had presumed that getting a gap in the pts within the framemd5 was corresponding with the buffer overrun error in the terminal output. I’ve tested a few hours of recorded with your patch applied and haven’t gotten any pts discontinuity in the framemd5s yet.


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