How to use AVAssetReader and AVAssetWriter for multiple tracks (audio and video) simultaneously?

Question

I know how to use AVAssetReader and AVAssetWriter, and have successfully used them to grab a video track from one movie and transcode it into another.

Answer 1

Have you tried using two AVAssetWriterInputs and pushing the samples through a worker queue? Here is a rough sketch.

processing_queue = dispatch_queue_create("com.mydomain.gcdqueue.mediaprocessor", NULL);

[videoAVAssetWriterInput requestMediaDataWhenReadyOnQueue:myInputSerialQueue usingBlock:^{
    dispatch_asyc(processing_queue, ^{process video});
}];

[audioAVAssetWriterInput requestMediaDataWhenReadyOnQueue:myInputSerialQueue usingBlock:^{
    dispatch_asyc(processing_queue, ^{process audio});
}];