Support additional container formats for VP8/9

[cyberj0g]

As LPMS support for VP8 and VP9 is added by this PR, we need to support containers compatible with these codecs. I propose enabling WEBM and MKV support in production libavcodec bulid. It will require adding something like that to ffmpeg build arguments:

--enable-demuxer=matroska,webm,opus

We support hardware accelerated VP8/9 decoding, but not encoding, therefore, only viable route is .mkv or .webm input and .mp4 or .ts output. We need to enable Ffmpeg's internal opus demuxer (and maybe vorbis) to support WEBM, which won't come with AAC audio. MKV support is feasible as it's a very common container format too. I'm not sure if we are interested in supporting WEBM DASH, given streaming is handled by Mist server. The question is, how .webm and .mkv would be split into segments for transcoding?

[darkdarkdragon]

Shouldn't we also enable opus codec? I suspect main use case for VP8 will be to take in WebRTC stream (with VP8/opus) and transcode it into h264/aac.

The question is, how .webm and .mkv would be split into segments for transcoding?

It is not the job of go-livepeer node to split files (.web, .mkv) into segments.

[Thulinma]

Isn't the Opus demuxer only for .opus files? As far as I know, the matroska demuxer can handle Opus inside .mkv just fine without further requirements (but I could be wrong about this...).
Oh, perhaps good to know: webm is a strict subset of matroska. So the matroska demuxer can handle that by itself, too.

Not supporting DASH seems reasonable (and sensible) to me. 👍
If you're doing MP4/TS outputs, plain HLS of course works just fine. It would however be nice to (optionally?) support MKV format outputs as well, as the overhead is much smaller than with MP4 or TS, and parsing that format uses less RAM/CPU. It would give a decent performance boost 🙂. Of course that is something that could be added at a later date as well (perhaps when we move to a fully-streaming workflow?).

[darkdarkdragon]

Didn't know that webm is a subset of matroska. Then it makes sense to enable them both for input and output.

[cyberj0g]

Thanks for the input. I like the idea of including MKV (and WEBM) support. WEBM demuxer and muxer still needs to be explicitly enabled. Currently, relevant Ffmpeg options for production build look like this (HW codecs are included separately):

    --enable-encoder=aac,opus,libx264 \
    --enable-decoder=aac,opus,h264 \
    --enable-muxer=mpegts,hls,segment,mp4,hevc,matroska,webm,null
    --enable-demuxer=flv,mpegts,mp4,mov,webm,matroska

https://github.com/livepeer/go-livepeer/blob/ip/hevc/install_ffmpeg.sh

[yondonfu]

Closed by #2135