I am writing an MP4 file from a video recording.
I'd like to understand how large this file is getting during the recording itself so that I can warn the user if the file is close to exceeding the amount of available space on the device.
Is there a way to do this prior to finishing writing the file? I understand that AVCaptureFileOutput has a maxRecordedFileSize (which would obviate the need for me to estimate the file size in the first place) but I have to use AVAssetWriter in this case since I need access to the individual frames' sample buffers during the recording for some real-time image processing.
One attempt I've made is to try calling CMSampleBufferGetTotalSampleSize() on each audio and video sample buffer that is successfully appended to its corresponding AVAssetWriterInput, and add these up. However, the resulting size is 10x smaller than what I get if I check FileManager.default.fileSize(atPath:) after the file has finished writing.
Are there any other options here?