Re: Transcoding audio with MediaRecorder

On 03/12/2015 12:29 AM, Ashley Gullen wrote:
> I have been experimenting with Firefox's Web Audio (decoding) and
> MediaRecorder (encoding) APIs to transcode audio between formats, such
> as transcoding a .wav file to Opus in the browser. A file can be
> decoded with the Web Audio context's decodeAudioData, and the
> resulting buffer connected to a media stream destination node, whose
> stream can be recorded with MediaRecorder.
>
> The big problem is this can only transcode audio in real-time. For a
> tool based on this to be useful, it should be able to transcode as
> fast as it can. This suggests the use of an OfflineAudioContext, but
> these cannot create media stream destination nodes (at least in
> Firefox, when I tried). It's not clear to me, but I get the impression
> a MediaStream is a real-time stream and cannot go faster-than-realtime
> anyway.
>
> Does there need to be a new API to enable this?

At the moment, the MediaStreamTrack concept doesn't offer any time
manipulation; it is assumed to run in real time, or as close to it as
synchronization can manage.

Allowing a MediaStreamTrack to run in another time mode is an
interesting idea - it would, at a minimum, require access to the
implicit clocks of the media stream - but I don't think we have any
chartered work items that look at this issue at this time.

Haral

Received on Thursday, 12 March 2015 06:59:38 UTC