On iOS 11, encoding a frame may return error with log
"Error encoding frame 0", which means vtenc_output_callback
is called with status=0 and sample_buffer=NULL. Then the
encoding session will be crashed on next callback wether or not
closing the codec context.
Let us look through the link below introducing VTCompressionOutputCallback,
https://developer.apple.com/documentation/videotoolbox/vtcompressionoutputcallback?language=objc
"status=0" (noErr) means compression was successful.
"sampleBuffer=NULL" means the frame was dropped when compression
was successful (status=0) or compression was not successful (status!=0).
So we should not set AVERROR_EXTERNAL on "status=0" and "sample_buffer=NULL"
as it is not a error.
The fix is that we only set AVERROR_EXTERNAL with status value non zero.
When sample_buffer is NULL and status value is zero, we simply return
with no other operation.
This crash often occurs on iOS 11 for example encoding 720p@25fps.
Signed-off-by: sharpbai <sharpbai@gmail.com>
Signed-off-by: Rick Kern <kernrj@gmail.com>
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