[FFmpeg-devel] [PATCH] issue251, xvid within .ogm will not remux to .avi

[Måns Rullgård]

Michael Niedermayer <michaelni at gmx.at> writes:

> On Mon, May 26, 2008 at 07:29:40AM +0100, M?ns Rullg?rd wrote:
>> Michael Niedermayer <michaelni at gmx.at> writes:
>> 
>> > Hi
>> >
>> > The patch below will fix remuxing from some ogm. Iam not 100% sure that
>> > this is the correct solution though ...
>> 
>> I believe you, but could you please explain a little.
>
> Where should i start ...
>
> The mpeg4 stream in this ogm uses these infamous packed b frames which avi
> with some demuxers needed.
> This should make pts=dts of the packets.
>
> Now, the first packet that comes out of the ogg demuxer for the video stream
> had a pts=0
> Then it returned 7 packets with pts=AV_NOPTS_VALUE
> and then a packet with pts=7
>
> This cannot be correct as there are just 6 distinct pts values between 0 and
> 7. (and packed b frames means the stream should behave as if pts=dts and
> theres no frame reordering)

In that case, the file is invalid.

> droping the first timestamp (or using -1) is the smallest change which fixes
> the issue. I do not know what the correct timestamps are supposed to be. 

Discarding information from valid files (all ogg files, not just ogm)
for the sake of one broken ogm file is unacceptable.

> I do not even know if the "timestamps" in ogm are pts or dts ...
> AFAIK there is no OGM spec?

I've never seen one...

-- 
M?ns Rullg?rd
mans at mansr.com