898396 - Media Recording - MediaRecorder's mimeType attribute maybe null after call the start()

Status: RESOLVED INVALID

(Core :: Audio/Video: Recording, defect)

Description

[Randy Lin [:rlin] - Be Mozillian on 2015/01/26]

We set the mimeType when encoder return the first data, so there is a timing issue to cause this value to be null.

Comment 1

[Randy Lin [:rlin] - Be Mozillian on 2015/01/26]

Hi Roc,
Should we make mimeType decision in 
MediaRecorder:start() function by...
1. User set mimeType preference (not done yet) 
2. check the mediaStream has 
  1. only has video track ->imply record the video/webm or ??
  2. only has audio track ->imply record the audio/ogg
  3. both->imply record the video/webm or ??

Or let the encoder choose the suitable mimetpye form mediaStream?

Comment 2

[Robert O'Callahan (:roc) (email my personal email if necessary)]

We need to let the encoder choose the MIME type based on the MediaStream, and we can't do that synchronously in start().

Comment 3

[Randy Lin [:rlin] - Be Mozillian on 2015/01/26]

I set this issue to be invalid due to the mimeType would be provided when the encoder start to pass out the encoded data.

Comment 4

[Jason Smith [:jsmith]]

(In reply to Randy Lin [:rlin] from comment #3)
> I set this issue to be invalid due to the mimeType would be provided when
> the encoder start to pass out the encoded data.

But how would a web developer know that? Shouldn't we have an onXXX handler to give a web developer knowledge that the mime type has been populated and be ready for use?

Comment 5

[Jason Smith [:jsmith]]

Looking at the spec, the only event handler that might be a potential candidate here to use would be the onstart event handler. Do we need to implement support for that event handler here to allow a web developer to know the mime type is ready for use?

Comment 6

[Robert O'Callahan (:roc) (email my personal email if necessary)]

I think probably the MIME type should only be available when the first Blob is delivered.