AV Foundation - AVAssetTrack, mediaType & CMFormatDescriptio

Question

I have a quicktime object i am reading with av foundation. I can see it's tracks and I would like to be able to read the 'tmcd' track (timecode) and get it's output as a string i can use in an NSTextView.

With an NSLog and a [track formatDescriptions] i see:

{\n\tmediaType:'tmcd' \n\tmediaSubType:'tmcd' \n\tmediaSpecific: {\n\t\tframeDuration: {1001/24000 = 0.042}\t\tframes/sec: 24\t\ttcFlags: 0 \n\t} \n\textensions: {{type = immutable dict, count = 1,\nentries =>\n\t1 : {contents = \"VerbatimSampleDescription\"} = {length = 38, capacity = 38, bytes = 0x00000026746d63640000000000000001 ... 03e918d400000000}\n}\n}\n}" )

I can can see there is a lot of information in there, but I wonder how I can use this. Is this something I can pull apart with other AV Foundation tools or do I need to break it apart somehow?

Basically I would like to end up with a format such as "00:12:23:12"

Thanks!

Adam

Despite my answer below: does anyone have an information what VerbatimSampleDescription can tell me? How can one breakdown the codes in there? — konran, May 28 '13 at 07:48

score 1 · Answer 1 · answered Jul 17 '16 at 16:34

Try using avfprobe. It will decode all of the track info for you, including the CMFormatDescription that you mentioned in your question. You'll see something like this:

formatDescriptions = [
    {
        mediaType = kCMMediaType_TimeCode; // = 'tmcd'
        mediaSubType = 'tmcd';
        extensions = {
            VerbatimSampleDescription = <00000022 746d6364 00000000 00000001 00000000 00000002 0000ea60 000003e9 3c00>;
        };
    },
    ];

However, this is just info about the timecode track -- not the contents of the track. I also don't have any more information about the contents of the VerbatimSampleDescription property.

that's a handy set of classes, @MatthewSelf ! – Fattie Dec 15 '18 at 14:03 — Fattie, Dec 15 '18 at 14:03

score 0 · Answer 2 · answered May 28 '13 at 07:47

You could try this:

NSArray*                        arrFormat   = [tTrack formatDescriptions];
NSInteger                       nCountArr   = [arrFormat count];
CMTimeCodeFormatDescriptionRef  refCmFormat = (__bridge CMTimeCodeFormatDescriptionRef)(arrFormat[0]);
NSDictionary*                   dictFormat  = (__bridge NSDictionary *)(refCmFormat);

NSLog(@"format[%ld] = %@", nCountArr, dictFormat);

In dictFormat you get keys and values for your not well readable formatDescriptions string abobe. Then have a look, what keys/values you need...

AV Foundation - AVAssetTrack, mediaType & CMFormatDescriptio

2 Answers2