When using an HDMI recorder with getUserMedia and sending the stream to a MediaRecorder (with the patch from bug 1409727 applied, and the media.recorder.video.frame_drops pref flipped), I usually get 35 to 50 frames per second in the resulting recordings captured on my macbook. After changing the setAlwaysDiscardsLateVideoFrames parameter at http://searchfox.org/mozilla-central/rev/40e8eb46609dcb8780764774ec550afff1eed3a5/media/webrtc/trunk/webrtc/modules/video_capture/mac/avfoundation/video_capture_avfoundation_objc.mm#198 to "NO", I consistently get 60fps. The frame pacing is very irregular though: 3ms 6ms 21ms 3ms 50ms 20ms 8ms 10ms 20ms 6ms 47ms 11ms 14ms 13ms 11ms 4ms 34ms 9ms 22ms 7ms 5ms 15ms 47ms 6ms 19ms 4ms 3ms 16ms 54ms 5ms 20ms 3ms 3ms 17ms 53ms 4ms 16ms 3ms 4ms 24ms 3ms 51ms 17ms 3ms 2ms 26ms 4ms 48ms 23ms 5ms 4ms 21ms 3ms 49ms 17ms 4ms 3ms 26ms 4ms 38ms 4ms 4ms The alwaysDiscardsLateVideoFrames documentation: https://developer.apple.com/documentation/avfoundation/avcapturevideodataoutput/1385780-alwaysdiscardslatevideoframes An Apple Technical Note that seems very relevant: https://developer.apple.com/library/content/technotes/tn2445/_index.html
I seem to recall pehrsons having a look at this one. Florian, how important is this?
Priority: -- → P2
Yeah, we investigated florian's frame drops on IRC and it led to this. An analysis of why we're causing these frames to drop would be good (are we too slow, then why and how slow?), including if we can do anything simple to avoid it. Also how many devices would be affected -- in particular the built-in ones in macbooks. Then we'd have to figure out what impact flipping this to "NO" has in terms of memory consumption and growth in a worst case.
(In reply to Paul Adenot (:padenot) from comment #1) > Florian, how important is this? Not dropping frames is important for the accuracy of my frame recording based performance tests. There are 2 possible approaches here: - add an about:config pref so that I can just flip it when running my tests. - figure out why we are slow, and fix it to possibly make this benefit all Mac users. The lost frames don't seem related to trying to reach 60fps: when my HDMI recorder was set to generate 30fps, we were still losing some.
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