Encoding FFMPEG to MPEG-DASH – or WebM with Keyframe Clusters – for MediaSource API

Question

I\'m currently sending a video stream to Chrome, to play via the MediaSource API.

As I understand it, MediaSource only supports MP4 files encoded with MPEG-DASH, or

Answer 1

To ensure every cluster in your WebM starts with a keyframe, try something like this:

ffmpeg \
  [...inputs] \
  -vcodec libvpx \
  -keyint_min 60 \
  -g 60 \
  -vb 4000k \
  -f webm \
  -cluster_size_limit 10M \
  -cluster_time_limit 2100 \
  [...output]

Basically, as implemented, every keyframe has to be at the beginning of a cluster but the inverse is not true. That is, on key frame there will be a new cluster, but on new cluster there won't necessarily be a keyframe. To get around this issue, we simply set the cluster size to something large that we'll never hit.

In this example, we'll have a keyframe every 2 seconds, and the cluster time limit is 2.1 seconds, so we'll never hit it. The bitrate is 4Mbit, and the cluster size limit is 10M-something. Not sure if it's bit or byte there but it doesn't matter as we'll never hit it as I've set it much greater than it needs to be.