Hey everyone, I wondered if anyone had experienced this or had a potential fix.
I sometimes get asked to stream to Facebook Live for clients or to Vimeo Live and have experieinced a weird issue with audio sync.
We delay the audio coming out of the console and play a sync test down the stream to ensure that the video and audio are all good before the show and then monitor for the duration of the stream. No worries.
But when we come to watch the online recording (so a Facebook stream saved to a page, or a vimeo stored video) the audio is now out of sync, despite it being fine live.
Has anyone encountered this? Using a Pearl, we’re streaming at 1920 x 1080 30fps 2500kbs AAC 44khz 256kbs.
There are a few possibilities for an A/V sync issue. The most common ones would be encoding settings and network bandwidth.
The encoding settings you have listed below may be an indication of the issue:
1920 x 1080
30fps 2500kbs
AAC 44khz 256kbs.
The video bitrate you mention is 2500kbps, which is closer to the minimum requirement for 1280 X 720 resolution. The increased compression with a much larger frame size of 1920 X 1080 could be causing the issue.
When streaming with Full HD resolution of 1920 X 1080 we recommend a minimum video bitrate of 6500 kbps, but more ideally 8000 - 10000 kbps.
Another possibility, especially for Facebook is that Facebook specifically requests in its encoding profile that the audio be AAC 44 kHz at 128 kbps
If you have the network bandwidth to support a higher video bitrate, I would highly recommend both increasing the video bitrate to a minimum of 6500 kbps for Full HD and changing the audio bitrate to 128 kbps. This should likely provide a more correct and stable AV Sync.
If increasing the bitrate is not possible, then I would recommend decreasing your frame size to 1280 X 720 and changing the audio bitrate to 128 kbps.
If the issue continues to occur, ensure on a local recording that the Audio and Video are in fact in synchronization. If the A/V is arriving to the Pearl out of sync it will need to be adjusted through the audio inputs section using the -300 to +300 milliseconds adjustment options.
If the AV sync is correct locally on Pearl, and the encoding settings are correct and you are still seeing an AV sync, the issue is highly likely to be network related. This would be caused either by a firewall throttling connection speeds causing packet loss or if you are maxing out your upload bandwidth for a stream you would also see packet losses which would break the AV Sync
This information is very helpful as we have had AV sync issues in our live streams.
We are using BirdDog P200 NDI cameras that have 1080p30 bandwidth that maxes out bandwidth at “180” (I presume Mbps). We are using 3 cameras in our main stream, however, we have a total of 5 cameras on the network - all of which have been entered as NDI sources on our Pearl-2. I have dialed back the 3 primary cameras to 150 and the remaining 2 to 100. All totaled, that should put our bandwidth at 650 Mbps. Our Dashboard page shows the following:
Obviously, we are pushing the limits on the network, but there isn’t much else fighting for bandwidth. My question is in regard to setting YouTube upstream bitrate on the Pearl-2. Should we set it for auto (which we have in the past and had issues), or should I manually set it for something like 12000 Mbps? Our upstream is 20 Mbps, so we would still be well under our maximum upload speed.
The Channel’s encoding bitrate would be based on the overall frame size and desired quality. If you are sending a single 1920 X 1080 frame size stream to Youtube, you could certainly set the video bitrate anywhere between 8000 and 12000 kbps and still be fine for bandwidth - theoretically speaking
