Temp file used in AVAssetWriter/AVAssetWriterInput

I use AVAssetWriter and AVAssetWriterInput to capture the input (CMSampleBuffer) to a target local file. It seems that it always writes to a temporary file first and write to the actual target file after finishWriting() is called. Is there a way to write to target file directly instead of to a temporary file. It is not using multi-pass now.


Now, it causes a problem if the app crashes, and the recorded media can't be recovered. We like to at least recover the media.


Thanks

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CasperTheOne
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I recently noticed that (on macOS) setting 

shouldOptimizeForNetworkUse = YES
on the 
AVAssetWriter
instance triggers the behaviour you are describing: Media sample data is written to temporary file (in the same location, with some random characters added to the file name), and only in 
finishWriting
the final file is written, presumably by first writing the movie header and then appending the sample data from the temporary file (which would explain why the run time of 
finishWriting
depends on the size of the video data).

Without 

shouldOptimizeForNetworkUse
, no temporary file is created and 
finishWriting
returns in constant time.


Even if 

shouldOptimizeForNetworkUse
is not involved in your case, there may be other properties that trigger this behaviour. Judging from the documentation, 
movieFragmentInterval
may be a candidate that is relevant for your setup.
Posted by
NoHalfBits
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finishWriting() will trigger the header of your file to be written so your file isn't readable before that anyway... (unless you're using segmented mp4)

Posted by
Valerian
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It seems what trigger by finishWriting() is more than the header. The header generally shall be small. However, the real situation is, the larger the video being recorded, the longer the wait time to the callback is necessary.

Posted by
CasperTheOne
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I recently noticed that (on macOS) setting 

shouldOptimizeForNetworkUse = YES
on the 
AVAssetWriter
instance triggers the behaviour you are describing: Media sample data is written to temporary file (in the same location, with some random characters added to the file name), and only in 
finishWriting
the final file is written, presumably by first writing the movie header and then appending the sample data from the temporary file (which would explain why the run time of 
finishWriting
depends on the size of the video data).

Without 

shouldOptimizeForNetworkUse
, no temporary file is created and 
finishWriting
returns in constant time.


Even if 

shouldOptimizeForNetworkUse
is not involved in your case, there may be other properties that trigger this behaviour. Judging from the documentation, 
movieFragmentInterval
may be a candidate that is relevant for your setup.
Posted by
NoHalfBits
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