Automatic conversion of aac to m4a

[Nick Ludlam]

On 14 Mar 2011, at 15:13, Andy Bircumshaw wrote:

> On 14 Mar 2011, at 09:42, <shevek at o2.co.uk> <shevek at o2.co.uk> wrote:
>> Why introduce a new tool into get_iplayer? 
>> 
>> Ffmpeg can do this already. 
>> 
>> See my post [1] for details
>> 
>> I agree with the --m4a option but I think it should use ffmpeg
> 
> 
> Absolutely agree that no further deps should be added to get_iplayer unless we're sure they're necessary.
> 
> Surely it must be possible with the tools we have already to remux properly.
> 
> Maybe ffmpeg has a --flag that will allow it to produce compatible files?
> 
> It doesn't seem like this option has yet been thoroughly explored.
> 
> I'm not sure that --m4a option is necessary, as the current .aac files (or their container, specifically) are known to be broken. There are a number of players they don't work on, and they only play on the systems they do because these OSS players (VLC, mplayer) are particularly forgiving.

Agreed, I'm only using an additional flag while I'm working on the tests, and I personally feel like m4a is a more appropriate container format for end users than raw aac, as it should be compatible with a wider range of players. As Richard Hughes suggested, we can also make ffmpeg transcode into mp3, for those who just want things to work with the minimum of dependencies.

I'll certainly have a look at using ffmpeg for m4a muxing if at all possible, but I actually want a practical solution which balances my available time against runtime dependencies, and I know mp4box works well, and is suitably cross platform.

I'm very happy to take input from those who are more knowledgable about ffmpeg's remuxing capabilities, but dinkypumpkin suggested the "aac_adtstoasc" bitstream filter doesn't work very reliably.

Nick