[FFmpeg-devel] [PATCH] libavformat/aac: Parse ID3 tags between ADTS frames.

[Richard Shaffer]

On Fri, Feb 2, 2018 at 5:52 AM, James Almer <jamrial at gmail.com> wrote:
> On 2/1/2018 11:37 PM, rshaffer at tunein.com wrote:
>> From: Richard Shaffer <rshaffer at tunein.com>
>>
>> While rare, ID3 tags may be inserted between ADTS frames. This change enables
>> parsing them and setting the appropriate metadata updated event flag.
>> ---
>> I have encountered a streaming provider that I must support which does this.
>> There are indications that it isn't totally off the wall, and that it does
>> happen in the wild:
>> * https://www.w3.org/TR/mse-byte-stream-format-mpeg-audio/
>>   (See specifically sections 3 and 4.)
>> * https://github.com/video-dev/hls.js/issues/508
>>
>> That being said, the providers that do this are in the minority. It seems most
>> streaming providers will do one of the following:
>>  1. If using .aac segments inside of HLS, use the #EXTINF for text metadata and
>>     use an ID3 tag at the head of the segment for things like timing metadata.
>>  2. If streaming raw AAC over HTTP, use Icy metadata.
>>
>> Aside from comments on the code, I'd be interested in any opinion about whether
>> this is something that should or should not be supported in libavformat.
>>
>> Thanks,
>>
>> -Richard
>
> Can you provide a sample and add a fate test for this? To avoid
> regressions in the future. This demuxer still needs some work.
>
> Use the new probetags() function you added in your other id3v2 test if
> the tags between samples in the file are the only ones, or if they
> differ in some way from the ones at the beginning of the file, so
> ffprobe will report them instead.
> Alternatively, see fate-adts-demux in tests/fate/demux.mak

Oh, somebody did merge that test. How cool.

I don't think we can test this with ffprobe, though. It will just read
tags at the head of the file and not in the middle.

I have at least one sample that's ok for me to share. I'll work on a
separate patch to add a fate test.

-Richard

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