[Libav-user] QTKit -> Libav: has it ever been done?

Brad O'Hearne brado at bighillsoftware.com
Wed Mar 27 04:50:08 CET 2013

In lieu of having no luck over several weeks getting video + audio samples captured from QTKit resampled and encoded with Libav to FLV (with video), I've kind of hit a bit of a brick wall. The runnable Mac app and source demonstrating this use case hasn't apparently shed any light on why the audio being encoded is junk. While my gut all along has been that there's something relatively simple at work, perhaps a pointer problem or something, at the same time I've been over this fairly modest section of code so many times I'm not sure what more to try. 

Again, my use case: 

QTKit capture (audio / video) -> convert (video)/resample (audio) -> encode to FLV -> output (file or network stream)

Up to this point, I've assumed all of the problem was in my code. I still don't doubt that is likely the case, but given no headway looking for the problem there, or to whatever degree anyone else has taken a look at the sample app I provided it also hasn't rendered any real headway, I started looking in other media libraries which either depend or appear to partially depend on Libav. Basically what appears to be the case is that they don't use Libav on the other side of QTKit capture, so as of now, I am not aware of any example which is publicly available demonstrating that this has been done. 

So at this point, it seems a decent question to consider if maybe the problem lies in Libav. I think there's a pretty simple question to ask: has a QTSampleBuffer ever been used to fill a sample array, resampled, and encoded to FLV? -- i.e. does anyone actually know if this works? If so, I would be much obliged if you could direct me to the unit test or code example which demonstrates this, and I should be able to figure out what deficiency exists in my code. If such a unit test or code example does *not* exist, then I guess a question for the maintainers -- what do you think the chances are that there's a bug somewhere in either resampling or the adpcm_swf codec that could be affecting audio? 

Thanks, I greatly appreciate it.


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