[FFmpeg-soc] [PATCH] xiph packetizer

[Josh Allmann]

Hi,

On 27 July 2010 03:03, Martin Storsjö <martin at martin.st> wrote:
> On Mon, 26 Jul 2010, Josh Allmann wrote:
>
>> This version works better, but is not yet complete.
>>
>> -The scaffolding for Vorbis is mostly up, but I have to set its SDP properly.

Done.

>> -Theora video has problems with I-frames (or whatever the Theora
>> equivalent is), and exhibits serious blocking in areas of motion.

Fixed, although on occassion it is a bit wonky. The depacketizer will
complain about a missing start fragment at a particular position in
big buck bunny, disrupting the video briefly, but otherwise it is
fine.

>> I hope this is due to some invalid reads that Valgrind complains about.

Valgrind fixed.

>> -Packing multiple frames in a single packet is another TODO.
>

Not yet complete, but is not critical for proper operation, either.

> A few comments:
>
> +    /* set xiph data type */
> +    switch (*buff) {
> +        case 0x01:   // vorbis id
> +        case 0x05:   // vorbis setup
> +        case 0x80:   // theora header
> +        case 0x82:   // theora tables
> +            xdt = 1; // packed config payload
> +        case 0x03:   // vorbis comments
> +        case 0x81:   // theora comments
> +            xdt = 2; // comment payload
> +        default:
> +            xdt = 0; // raw data payload
> +    }
>
> I guess you want break statements in the switch, too...
>

Fixed.

> +    /* set ident
> +     * Probably need a non-fixed way of generating
> +     * this, but it has to be done in SDP and passed in from there. */
> +    q = s->buf;
> +    *q++ = 0xfe;
> +    *q++ = 0xcd;
> +    *q++ = 0xba;
>
> I haven't read the specs, but what's the role of this ident code? Is there
> any harm in having it hardcoded to a specific value? Is it set in the
> original stream data somewhere, so that you'd have to parse out the
> correct value from there? Or is it only used to distinguish streams if you
> have more than one vorbis/theora stream in the same presentation? In that
> case, you could use e.g. one hardcoded value for vorbis and another for
> theora - that would probably be enough for some time at lesat.

As Luca said, it is only used to make sure the extradata doesn't
change mid-stream. Different streams can have the same ident, eg a
Vorbis and a Theora can share 0xfecdba. Our depacketizer doesn't
handle changing the ident anyway.

Revised patch attached. I also had to enlarge the outgoing RTSP buffer
to handle the SDP extradata.

Josh
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