[FFmpeg-devel] [PATCH] Add libavsequencer.

Sebastian Vater cdgs.basty
Thu Aug 19 22:02:11 CEST 2010

Vitor Sessak a ?crit :
> On 08/19/2010 12:04 AM, Ronald S. Bultje wrote:
>> Hi,
>> On Wed, Aug 18, 2010 at 5:58 PM, Stefano Sabatini
>> <stefano.sabatini-lala at poste.it>  wrote:
>>> So in the end I suggest this course of action: apply the lavseq patch,
>>> *or* if we want to add more stuff to it before to commit it, then
>>> maybe we should focus on the BSS. Once that's ready, we can create
>>> lavseq *and* immediatly commit the BSS definition.
>> I don't want anything committed until I've seen all patches required
>> for TCM playback posted to ffmpeg-devel so we can judge whether each
>> component is actually necessary.
>> I don't want duplicate code, I don't want overly complicated code and
>> I don't want overdesigned code. I want exactly that code necessary for
>> TCM playback. Nothing more. Those patches, we will review together,
>> removing things that are unneeded/unused, removing code available
>> already elsewhere in FFmpeg, and simplifying it to the best of our
>> ability. Once that process is done, we can commit the individual
>> parts.
> I've read the whole thread, and I really think this is a great idea.
> Indeed, let's see a patch (as big as it needs to be, _but not bigger_)
> to make playing TCM files work. That means that _every_ field in
> _every_ structure should be:
> (a) written by some code in the patch
> (b) read by some code in the patch
> Everything that is there for the future, for editors, for
> visualization and for transcoding should be added _later_ (but maybe
> it is a good idea to keep it in your tree). As I said, simpler patches
> are approved faster, so let's make this patch as simple as possible
> (and the simpler way by now is with no new library).

To summarize that for the different parts of avseq:
1. The BSS:
All fields are required (since TCM uses them all).

2. The player:
Most fields are required (some commands are unimplemented right now, due
to a lack of editor and properly and easy testing of it), I've marked
today all (hope didn't miss anything out) these parts with a TODO in the
effect execution path.

This mainly regards the hold / decay stuff which I added for the MED
demuxer / decoder in TuComposer, which however, never got implemented
because in the time I wanted to start it was the time where I already
recognized that it made no sense to continue old TuComposer as Amiga-only.

But MED demuxer / decoder will come into FFmpeg.

3) The mixer:
Start with the low quality mixer only. The null mixer is not required
here, since there's a) no seeking here and b) no hardware mixing support

Also remove the multiple mixer support until we a) actually need null
mixer or/and b) have a hardware mixer ready.

Besides this, I'll try to edit my wxTuComposer GUI in parallel, so we
get the editor advanced as well as the FFmpeg stuff. The editor will
allow us a) to test everything in the final state and b) to see if our
current design really fits not only for transcoding / playback but also
for editing. ;)

Please note, that wxTuComposer will be a independent project of FFmpeg,
it will just be the first project from me that will use the new
avsequencer API. ;-)

It will probably not only a full editor, but more like a wxWidgets GUI
class, which you can easily add to your own projects, i.e. create a
AVSequencer tracker instance with just two lines of C++ code:

wxTuComposer *tucomp = new wxTuComposer ();
tucomp->Show ();

The rest will be, as usual in wxWidgets just be event handling. ;-)

Maybe there is some day, where you'll find this on wxCode page of
wxWidgets. ;-)
Maybe even I start this directly as wxCode project (just disregard that
I would stick to SVN for that, don't really want to go back to SVN after
working with git the last three months ;-))

>> Committing one part without knowing how the next part uses it is about
>> the worst design nightmare possible.
> I agree also with this. The right way to review the BSS is seeing
> where and how each field is used.


One last question here, since my initial patch regarding basic lavseq
integration added a changelog entry (added libavsequencer). I would
change that to sth. like: Added libavsequencer (formerly known as

The point is here, that some people surely did heard of TuComposer in
the last 5 years, and in case they search for it, they should find at
least the FFmpeg page to know that's now named AVSequencer.

I think a small notice regarding this in changelog or is enough. But
maybe you have other opinions.

Just another point, Vitor. You surely remember our last discussions
regarding BSS data structs in ffmpeg-soc. You know I was afraid that
extending the fields (uint16_t to enum, int, etc.) was frightening me
because of no more able to save that 100% to any file format.

I just want to tell you here, that these afraids are actually pointless
(I talked to Stefano already regarding this some days ago). Since
IFF-TCM1, as I developed it, is easily extendable regarding that (how I
should forget that, again 10l to me).

To be short, just an example. Let's say we extend uint8_t flags of
AVSequencerSong to enum AVSequencerSongFlags (which will be int then,
thus adding usually more 24 bits).

Storing these in IFF-TCM1 is NO problem! Just to some small magic like:
first_8_bit_of_flags = get_byte(pb);

Then read the remaining stuff as of old IFF-TCM1, then the first new one
(let's say we extended to 32-bit):
flags  = get_byte(pb) << 8 | first_8_bit_of_flags;
flags |= get_be16(pb) << 16;

That should do it. Since IFF-TCM1 also has a version / revision field in
the MHDR iff tag, we should bump that up simply by one. ;-)

Or to say it simple, forget all my concerns about this! No new format
required, just some small extension to IFF-TCM1 demuxer / decoder and
we're fine.


Best regards,
                   :-) Basty/CDGS (-:

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