allow non-downloading pipeline to play without download rate monitoring.

allow non-downloading pipeline to play without download rate monitoring.
r110733 broke pipeline playback when pipeline doesn't need downloading.

BUG=none
TEST=trybots

[wjia(left Chromium), 2011-11-21 23:37:46]

Fix another breakage.

[scherkus (not reviewing), 2011-11-21 23:41:06]

vrk: want to review this?

[vrk (LEFT CHROMIUM), 2011-11-22 00:17:28]

wjia: What exactly was broken? Can you give a link to an example and/or bug #? I
don't understand what you are trying to fix.

[wjia(left Chromium), 2011-11-22 00:35:10]

vrk,

The video capture preview is broken. You can run "chrome
--enable-media-stream www.corp.google.com/~wjia/preview.html". After
r110733, it shows only one frame, then freeze.

Basically, the preview pipeline uses a dummy demuxer, a CaptureVideoDecoder
and VideoRenderer.

Wei

There is no bug filed. I found this when I was trying to test my other
patch.

On Mon, Nov 21, 2011 at 4:17 PM, <vrk@chromium.org> wrote:

> wjia: What exactly was broken? Can you give a link to an example and/or
> bug #? I
> don't understand what you are trying to fix.
>
>
http://codereview.chromium.**org/8625002/<http://codereview.chromium.org/8625...
>

[vrk (LEFT CHROMIUM), 2011-11-22 00:52:34]

Effectively your patch sets the WebMediaPlayerImpl's ReadyState to
HaveEnoughData at the beginning of playback. That means the hang is because of
something in the video capture code that is dependent on the HAVE_ENOUGH_DATA
state or the canplaythrough event.

Can you show me what part of the video capture code is dependent on
HaveEnoughData/canplaythrough?

[vrk (LEFT CHROMIUM), 2011-11-22 00:57:43]

> Can you show me what part of the video capture code is dependent on
> HaveEnoughData/canplaythrough?

I realized my question might be unclear, so rephrasing: Could you explain to me
specifically how the checked-in code caused a hang for you, and why firing
CanPlayThrough immediately after playback fixes it?

[wjia(left Chromium), 2011-11-22 01:07:14]

On Mon, Nov 21, 2011 at 4:57 PM, <vrk@chromium.org> wrote:

> Can you show me what part of the video capture code is dependent on
>> HaveEnoughData/canplaythrough?
>>
>
> I realized my question might be unclear, so rephrasing: Could you explain
> to me
> specifically how the checked-in code caused a hang for you, and why firing
> CanPlayThrough immediately after playback fixes it?
>
> r110733 hangs video capture preview because playback_rate_ in PipelineImpl
is always 0. Video capture doesn't have a concept of downloading (or those
parameters managed by download_rate_monitor_, such as TotalBytes,
BufferedBytes, etc). The bit rate returned by dummy demuxer would be always
0 (since it's dummy). This can be used as a flag to tell PipelineImpl that
there is no need to use download_rate_monitor_. Therefore, an immediate
call to OnCanPlayThrough solves the problem.

Basically, for pipeline without download control, it's needed to bypass
download_rate_monitor_.

Wei


>
http://codereview.chromium.**org/8625002/<http://codereview.chromium.org/8625...
>

[vrk (LEFT CHROMIUM), 2011-11-22 19:06:33]

Hi Wei, I did some investigation yesterday and this is actually part of a deeper
problem with WebMediaPlayerImpl and HTMLMediaElement. I'm working on a fix right
now!

[vrk (LEFT CHROMIUM), 2011-11-22 22:25:09]

I added a bug report for this in crbug.com/105163, and I have a CL out to fix
it: http://codereview.chromium.org/8661002 
This issue should probably be closed in favor of 8661002.