How to get the Start Timecode (SMPTE) of a Quicktime-Movie in Objective-C in 64-bit?

问题

I've been pulling my hair out over this.

I've found a few things here, but nothing actually seems to work. And the documentation is really limited.

What I'm trying to figure out here is how to get the start time code of a Quicktime movie in Objective-C from the timecode track, and getting a human-readable output from that.

I've found this: SMPTE TimeCode from Quick Time

It works perfectly in 32-bit mode. But it doesn't work in 64-bit mode because of the Quicktime API. The software I need to incorporate it into already has been and must continue to run 64-bit.

I'm losing my mind here. Anyone out there know about these APIs?

Ultimately, the goal here is to figure out the start timecode of the Quicktime because its needed to set the OFFSET in FCP-X XML files. Without it, the video files are brought in without audio (or, really, its just slipped a lot).

回答1:

Use AVFoundation framework instead of QuickTime. The player initialisation is well explained in the documentation: https://developer.apple.com/library/mac/#documentation/AudioVideo/Conceptual/AVFoundationPG/Articles/02_Playback.html#//apple_ref/doc/uid/TP40010188-CH3-SW2

Once your AVAsset is loaded in memory, you can extract the first sample frame number (timeStampFrame) by reading the content of the timecode track if present:

long timeStampFrame = 0;
for (AVAssetTrack * track in [_asset tracks]) {
    if ([[track mediaType] isEqualToString:AVMediaTypeTimecode]) {
        AVAssetReader *assetReader = [AVAssetReader assetReaderWithAsset:_asset error:nil];
        AVAssetReaderTrackOutput *assetReaderOutput = [AVAssetReaderTrackOutput assetReaderTrackOutputWithTrack:track outputSettings:nil]; 
        if ([assetReader canAddOutput:assetReaderOutput]) {
            [assetReader addOutput:assetReaderOutput];
            if ([assetReader startReading] == YES) {
                int count = 0;

                while ( [assetReader status]==AVAssetReaderStatusReading ) {
                    CMSampleBufferRef sampleBuffer = [assetReaderOutput copyNextSampleBuffer];
                    if (sampleBuffer == NULL) {
                        if ([assetReader status] == AVAssetReaderStatusFailed) 
                            break;
                        else    
                            continue;
                    }
                    count++;

                    CMBlockBufferRef blockBuffer = CMSampleBufferGetDataBuffer(sampleBuffer);
                    size_t length = CMBlockBufferGetDataLength(blockBuffer);

                    if (length>0) {
                        unsigned char *buffer = malloc(length);
                        memset(buffer, 0, length);
                        CMBlockBufferCopyDataBytes(blockBuffer, 0, length, buffer);

                        for (int i=0; i<length; i++) {
                            timeStampFrame = (timeStampFrame << 8) + buffer[i];
                        }

                        free(buffer);
                    }

                    CFRelease(sampleBuffer);
                }

                if (count == 0) {
                    NSLog(@"No sample in the timecode track: %@", [assetReader error]);
                }

                NSLog(@"Processed %d sample", count);

            }

        }

        if ([assetReader status] != AVAssetReaderStatusCompleted)
            [assetReader cancelReading];
    }
}

This is a little more tricky than the QuickTime API and there must be some improvement to the code above but it works for me.

来源：https://stackoverflow.com/questions/12083325/how-to-get-the-start-timecode-smpte-of-a-quicktime-movie-in-objective-c-in-64

标签

objective-c

cocoa

quicktime