[FFmpeg-devel] [PATCH] ALAC support in the MOV muxer

[Baptiste Coudurier]

Hi,

Jai Menon wrote:
> Hi,
> 
> This is an experimental way of adding alac support to the mov muxer. As of 
> now, it isn't meant for svn, but comments on doing this the "right" way are 
> welcome. Also the ISO media code for alac is set to an arbitrary value 65. 
> This is wrong but I couldn't find the value on mp4ra.org. Also, I don't have 
> access to Itunes(or a win32 machine)  and still reading the quicktime spec in 
> detail. So as of now, ffmpeg can mux/demux alac into an mp4 container. Any 
> info on this is appreciated but please note that even if it works, this may 
> be a completely wrong way of doing this. Maybe Baptiste would have something 
> to say.

Yes, for now mux into .mov and check that quicktime can read it.
We will see about .mp4 later. Does itunes/ipod/iphone need .mp4 ?

>> [...]
>
> --- isom.c	(revision 12931)
> +++ isom.c	(working copy)
> @@ -31,6 +31,7 @@
>      { CODEC_ID_MPEG4     ,  32 },
>      { CODEC_ID_H264      ,  33 },
>      { CODEC_ID_AAC       ,  64 },
> +    { CODEC_ID_ALAC      ,  65 },

You gotta be kidding ;)
Im strongly against adding non standard object types unless very
strictly needed.

>      { CODEC_ID_MPEG2VIDEO,  97 }, /* MPEG2 Main */
>      { CODEC_ID_MPEG2VIDEO,  96 }, /* MPEG2 Simple */
>      { CODEC_ID_MPEG2VIDEO,  98 }, /* MPEG2 SNR */
> Index: movenc.c
> ===================================================================
> --- movenc.c	(revision 12931)
> +++ movenc.c	(working copy)
> @@ -305,7 +305,7 @@
>      put_tag(pb, "frma");
>      put_le32(pb, track->tag);
>  
> -    if (track->enc->codec_id == CODEC_ID_AAC) {
> +    if (track->enc->codec_id == CODEC_ID_AAC || track->enc->codec_id == CODEC_ID_ALAC) {
>          /* useless atom needed by mplayer, ipod, not needed by quicktime */
>          put_be32(pb, 12); /* size */
>          put_tag(pb, "mp4a");

Is this atom really needed ? Even on latest ipod/iphone ?

> @@ -1508,6 +1508,11 @@
>          }else if(st->codec->codec_type == CODEC_TYPE_AUDIO){
>              track->timescale = st->codec->sample_rate;
>              av_set_pts_info(st, 64, 1, st->codec->sample_rate);
> +
> +            ///ALAC: set frame_size from extradata

Useless comment. Code is doing explicitly what you describe:

> +            if(st->codec->codec_id == CODEC_ID_ALAC)
> +                st->codec->frame_size = AV_RB32((st->codec->extradata+12));

[...]

-- 
Baptiste COUDURIER                              GnuPG Key Id: 0x5C1ABAAA
SMARTJOG SAS                                     http://www.smartjog.com
Key fingerprint                 8D77134D20CC9220201FC5DB0AC9325C5C1ABAAA
Phone: +33 1 49966312