[FFmpeg-user] Adaptive Streaming between heaac and lcaac

[Ronak]

> On Jun 22, 2018, at 4:45 PM, Ronak <ronak2121-at-yahoo.com at ffmpeg.org> wrote:
> 
> 
> 
>>> Hi,
>>> 
>>> We are trying to setup an adaptive stream across two heaac streams and higher order lcaac ones.
>>> 
>>> So we’d have something like so:
>>> 
>>> HEAACv2 44khz/32kbps
>>> HEAACv2 44/64
>>> LCAAC 44/128
>>> LCAAC 44/256
>>> LCAAC 44/320
>>> 
>>> I setup a test stream this way and I’m seeing some problems.
>>> 
>>> Exoplayer is seeing this stream as not being able to support seamless adaptive switching because the defaultSampleDurations in the HE-AACv2 fMP4's moof boxes is 2048 while the LC-AAC file has 1024.
>>> 
>>> Why does HE-AACv2 have a higher sample duration when the sampling rate is supposed to be 44100, equivalent to the sampling rate of the LC-AAC audio?
>>> 
>> 
>> 
>> Has anyone ever tried to do this before? Is this a problem with how ffmpeg is generating the HEAACv2 fmp4 files?
>> 
>> 
> 
> 
> Could anyone please shed any light on why the defaultSampleDurations in moof are different between LC & HE-AAC at the same sampling rates?
> 
> 

I ran Apple's HLS mediafilesegmenter tool, and I can confirm that they set 1024 for the defaultSampleDurations in all moof segments for HE-AACv2 mp4s.

Can this be fixed in ffmpeg? I'm happy to send a patch to the devel mailing list to correct this.


Another interesting thing I saw is that their generated fMP4s don't include sidx boxes, since the stream is audio only created from an AAC file. 
Why does ffmpeg include sidx boxes? Can those be removed?

> 
>>> Thanks,
>>> 
>>> Ronak
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