[libbluray-devel] PTS and DTS of Blu-Ray titles made of multiple files

[John Stebbins]

On 11/11/2011 07:31 AM, Andrea3000 wrote:
> John Stebbins <stebbins at ...> writes:
>
>> Clips always have a PCR at the beginning.  So if FFmpeg is handling 
>> PCR discontinuities correctly, there really shouldn't be anything you
>> need to do.  However, I wouldn't be surprised at all if FFmpeg doesn't
>> handle them correctly.  I've never been very impressed with how 
>> FFmpeg handles timestamp processing.  That's one of the reasons
>> we keep our own TS demux in HandBrake.
>>
> I was wrong, FFmpeg doesn't seem to parse PCR field at all when using
> regular MPEG-TS demuxer. It reads PCR only when it uses raw MPEG-TS
> demuxer. But that demuxer doesn't provide proper packet parsing that
> is needed to properly decode every frame. Or at least I'm not able to use it..
>
> I think I need to implement this on my own, at ffmpeg level or at level
> of my app.
> But I have to study this MPEG-TS header structure a lot more because
> I still don't have a clear understanding of all the necessary pieces.
>
> One thing that I'm really not able to figure out is how I can handle
> seek properly. I mean, when I seek foreward, I
> don't know from which clip I am extracting packets after seek.
> If it were a stream without discontinuity, it's simply a matter of
> realigning to the new PTS and DTS values which are greater than the
> previous ones and are proportional to the playback time.
bd_tell_time() after the seek.  This will give you the absolute time in 90khz ticks of
your current position from the beginning of the title.  bd_seek() will always seek
to the nearest recovery point before the requested seek position.

> But with this type of stream, if I realign to the new PTS and DTS values
> I loose the playback time because new clip has its own PTS and DTS which
> start over and therefore I loose the actual position in the entire title.
> Does also PCR reset itself upon switching clip or it remains monotone?
They reset at the beginning of each clip.
.
> How can I always have an indicator of the relative position in the
> movie as long as PTS and DTS are no more suitable for this?
You can call bd_tell_time() at any point, but it will not always be 100% accurate.
It looks up your current position in the CPI which is an index of recovery
points in a clip.  So it will return the time of the nearest recovery point.

> Have I to use the number of bytes of the actual position compared to
> the total number of bytes of the entire title? This seems a dirty hack..
>
If I'm understanding your need correctly, bd_tell_time() should be adequate.

-- 
John      GnuPG fingerprint: D0EC B3DB C372 D1F1 0B01  83F0 49F1 D7B2 60D4 D0F7


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