[camera_avfoundation] fix stopVideoRecording waiting indefinitely and video lag at start

[misos1]

Call to startWriting was moved to startVideoRecordingWithCompletion to fix situation when completion is not called when _isRecording is YES but _videoWriter.status is AVAssetWriterStatusUnknown in stopVideoRecordingWithCompletion which can happen if stopVideoRecordingWithCompletion is called right after startVideoRecordingWithCompletion and didOutputSampleBuffer had no chance to call startWriting in meantime and to avoid lag which happens when is called startWriting between first frame creation and its appending.

Fixes flutter/flutter#132016
Fixes flutter/flutter#151319

Pre-launch Checklist

• I read the Contributor Guide and followed the process outlined there for submitting PRs.
• I read the Tree Hygiene page, which explains my responsibilities.
• I read and followed the relevant style guides and ran the auto-formatter. (Unlike the flutter/flutter repo, the flutter/packages repo does use dart format.)
• I signed the CLA.
• The title of the PR starts with the name of the package surrounded by square brackets, e.g. [shared_preferences]
• I linked to at least one issue that this PR fixes in the description above.
• I updated pubspec.yaml with an appropriate new version according to the pub versioning philosophy, or this PR is exempt from version changes.
• I updated CHANGELOG.md to add a description of the change, following repository CHANGELOG style, or this PR is exempt from CHANGELOG changes.
• I updated/added relevant documentation (doc comments with ///).
• I added new tests to check the change I am making, or this PR is test-exempt.
• All existing and new tests are passing.

If you need help, consider asking for advice on the #hackers-new channel on Discord.

[misos1]

Btw integration tests fail on my side with flutter packages main branch because here file.path for example ends with CAP_D5507C07-56E6-48E5-96F8-7D22FF8B5AB6.jpg but fileFormat.name is jpeg so file path does not end with file format name.

flutter: 00:55 +8: Capture specific image output formats
camera_avfoundation/example/integration_test/camera_test.dart:339
> expect(file.path.endsWith(fileFormat.name), true);

[hellohuanlin]

nit: isFirstSample

[hellohuanlin]

why is this check removed?

[misos1]

This is where it was not sending completion (in false case) so a dart future never resolved. But now startWriting is called at the same time as _isRecording is set to YES so finishWritingWithCompletionHandler in stopVideoRecordingWithCompletion can be called only after was called startWriting which sets _videoWriter.status to AVAssetWriterStatusWriting so that check is redundant (and again it would just indicate false possibility of not calling completion).

[misos1]

Actually maybe it should check whether status is AVAssetWriterStatusWriting and complete with error otherwise because it can be for example AVAssetWriterStatusFailed here (I suppose finishWritingWithCompletionHandler would just crash in that case). But this situation is nothing new introduced with this PR as before there was just check status != unknown which would pass failed to finishWritingWithCompletionHandler.

I also noticed check for AVAssetWriterStatusFailed in didOutputSampleBuffer where is called [self reportErrorMessage] but when I tried to force call reportErrorMessage I did not see this error report anywhere.

[misos1]

Regarding previous comment, seems finishWritingWithCompletionHandler is ok with AVAssetWriterStatusFailed it will just pass it to handler so there is no need to check whether is status not failed before calling it, it only has problem with AVAssetWriterStatusCancelled but there is no call to cancelWriting, AVAssetWriterStatusCompleted and AVAssetWriterStatusUnknown but these two also cannot happen.

[hellohuanlin]

do you intend to remove startWriting from didOutputSampleBuffer?

[misos1]

yes

[hellohuanlin]

Btw integration tests fail on my side with flutter packages main branch because here file.path for example ends with CAP_D5507C07-56E6-48E5-96F8-7D22FF8B5AB6.jpg but fileFormat.name is jpeg so file path does not end with file format name.

Seems reasonable to allow both jpg and jpeg to pass

[hellohuanlin]

I think it's reasonable change. Just some nit to make it easier for future readers.

[hellohuanlin]

Should this be isFirstVideoSample?

[hellohuanlin]

nit: "do not move startWriting call to didOutputSampleBuffer... "

Because there should only be 1 place to call startWriting.

[hellohuanlin]

can you also explain that this happens when stop video is called immediately after start, before the first video sample is arrived (if i understand correctly)

[hellohuanlin]

can you add a comment explaining that it's not necessary to check AVAssetWriterStatusUnknown anymore since we call startWriting immediately, even before video sample callback (please rephrase this).

[misos1]

ok, but such a comment loses context here because in sources it is not visible that there was such a check, only in this diff

[hellohuanlin]

nit: "so there's no need to check _videoWriter.status before finish writing"

[misos1]

Btw does this also require a second review?

[hellohuanlin]

Btw does this also require a second review?

Only first time contributors require a second review, so you are good to go. But feel free to tag more people as you see fit.

[misos1]

Oh ok (there are comments in my 2nd and 3rd PR that second reviews are required, but I did my first some year ago).

[hellohuanlin]

Only first time contributors require a second review, so you are good to go. But feel free to tag more people as you see fit.

Sorry I was terribly wrong - we need a second reviewer to land this.

[jmagman]

For the curious, from https://github.com/flutter/flutter/blob/master/docs/contributing/Tree-hygiene.md#getting-a-code-review

Every PR must be code-reviewed before check-in, including things like rolling a dependency. Getting a review means that a regular Flutter contributor (someone with commit access; see contributor access for details) has "approved" the PR in the GitHub UI. We call this "getting an LGTM" ("looks good to me").

If you are not yourself someone with commit access, then a second person with commit access must also review and approve your PR. This ensures that two people with commit access (trusted contributors) agree on every commit.

[bparrishMines]

LGTM

[hellohuanlin]

There's also a process to become a member: https://github.com/flutter/flutter/blob/master/docs/contributing/Contributor-access.md

If you are interested, I'm more than happy to sponsor it.

[misos1]

@hellohuanlin Ok so let's try it.