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Re: [mediacapture-record] Handle the case of audio/video track configuration changes (#188)

From: guest271314 via GitHub <sysbot+gh@w3.org>
Date: Sat, 21 Sep 2019 20:30:08 +0000
To: public-webrtc-logs@w3.org
Message-ID: <issue_comment.created-533828103-1569097807-sysbot+gh@w3.org>
@youennf Have not tried to change audio track configuration. Matroska and WebM supports variable resolution video input (https://gitlab.com/mbunkus/mkvtoolnix/issues/2582#note_189460892; https://gitlab.com/mbunkus/mkvtoolnix/commit/2548a7f3497940135e55be604a87b9495fdff94d; https://plnkr.co/edit/8J61Rw?p=info). Whether the implementation actually configures `MediaRecorder` (and corresponding HTML `<video>` element) to encode and render the input is a different matter. 

This PR https://github.com/w3c/mediacapture-record/pull/172 attempts to mandate that implementers encode the width and height exactly as input, instead of arbitrarily changing the encoding, that is, for example output for a handheld device.

When recording variable resolution input frames, from the front-end perspective, it is not a simple task to determine which portion of the implementer source code is not encoding or outputting the encoded resolution, either by way of a bug or deliberately. For more than a year had considered Chromium crashing when attempting to record an HTML `<video>` element using `captureStream()` being a bug in `MediaSource` implementation (TL;DR https://bugs.chromium.org/p/chromium/issues/detail?id=820997; https://bugs.chromium.org/p/chromium/issues/detail?id=943484; https://bugs.chromium.org/p/chromium/issues/detail?id=972470; https://bugs.chromium.org/p/chromium/issues/detail?id=983777; https://bugs.chromium.org/p/chromium/issues/detail?id=1004018; https://bugs.chromium.org/p/chromium/issues/detail?id=1001948). However, due to continued testing found that the output was intentional (https://bugs.chromium.org/p/chromium/issues/detail?id=983777#c25) which has the effect of impacting `getSettings()` result (even though `getSettings()` does not appear to be actually defined for `MediaStreamTrack` from `HTMLMediaElement.captureStream()`) where even though the underlying `width` and `height` of the current frame may have changed since the stream became active, only the initial `width` and `height` are set resulting in output inconsistent with input (https://plnkr.co/edit/n1rGNe?p=preview).

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