[FFmpeg-devel] LATM BitStreamFilter

Robert Swain robert.swain
Fri May 1 02:31:31 CEST 2009

Michael Niedermayer wrote:
> On Wed, Apr 29, 2009 at 08:21:06PM +1200, Paul Kendall wrote:
>> Can I ask why LATM is preferred as a bit stream filter rather than
>> as a decoder, or built into the AAC decoder, as ADTS is?
> A simple use case
> you have a demuxer that outputs AAC in LATM, and a muxer that doesnt
> allow LATM.
> Only a bitstream filter can fix this up in the current architecture unless
> you want to change it to allow multiple demuxers to be chained, in which
> case you could implement it as a demuxer too.

This may be an idea.

I think Paul was asking if the bitstream filters could only be inserted 
after encoding/before multiplexing and not after demultiplexing/before 
decoding which is where it is needed.

> Now if LATM supports multiple AAC streams and this would be actually used in
> practice then implementing it as a demuxer would be needed as a bitstream
> filter cannot have more than 1 stream as output.

It seems all instances in the wild at the moment use only one AAC stream 
per LATM stream. Is that right Paul?

> you seem fixed on only the goal of decoding, this is not good, we need
> to be able to remove as well as add LATM surrounding AAC.

The vast vast majority of people outside of DVB stream broadcasting do 
not need to add LATM. At least, I'm not aware of any other applications 
using LATM at the moment.

> If the remuxng case with LATM removial as well as keeping LATM doesnt
> work that would be reason to reject a patch.

I think different parts should be considered separately. That is, I 
think patches adding removal of LATM, addition of LATM or copying LATM 
should be considered separately and the lack of any should not hold up 
inclusion of any other as they're completely separate situations.

If Paul is willing to work on implementing everything under the sun for 
LATM, great. If he's only willing to work on removal of LATM, well, 
that's much better than nothing in my opinion and would cover most of 
the desired usage.

Creating LATM streams would mostly be of interest for people 
broadcasting DVB streams and they should have money to fund its development.

Also, decoding support is more important than encoding, isn't it?


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