What is 'forward continuous' and other questions about reverse playback.

[wl2776]

I am reading the GStreamer design documentation and have doubts while interpreting several sentences.
Probably, my problem is because English is not my native language.

The part-trickmodes.txt says in the "client side backwards trickmode" section:

 - A source plugin sends data in chunks starting from the last chunk of the
   file. The actual bytes are not reversed. Each chunk that is not forward
   continuous with the previous chunk is marked with a DISCONT flag.

What does 'forward continuous' mean?

For example, filesrc sends bytes from 150 to 200 in the first chunk and 100-150 in the second chunk.
Will it mark DISCONT the second chunk?

Going further, to the MPEG demuxer, processing a video file with I, P and B frames. How are they marked?

[ved kpl]

On Fri, Jul 30, 2010 at 1:17 PM, wl2776 <[hidden email]> wrote:

>
> I am reading the GStreamer design documentation and have doubts while
> interpreting several sentences.
> Probably, my problem is because English is not my native language.
>
> The part-trickmodes.txt says in the "client side backwards trickmode"
> section:
>
>  - A source plugin sends data in chunks starting from the last chunk of the
>   file. The actual bytes are not reversed. Each chunk that is not forward
>   continuous with the previous chunk is marked with a DISCONT flag.
>
> What does 'forward continuous' mean?
>
> For example, filesrc sends bytes from 150 to 200 in the first chunk and
> 100-150 in the second chunk.
> Will it mark DISCONT the second chunk?

   i guess  you meant 100-149.
   should not, since the 150-200 is continuous w.r.t 100-149.

> Going further, to the MPEG demuxer, processing a video file with I, P and B
> frames. How are they marked?

   GST_BUFFER_FLAG_DELTA_UNIT.
   http://www.gstreamer.net/data/doc/gstreamer/head/gstreamer/html/gstreamer-GstBuffer.html#GstBufferFlag

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[wl2776]

Thank you for the answer!
I'm really appreciate it, as I'm new to the MPEG-2 encoding, and there's not so much information about free libraries. Libmpeg2, for example, almost not documented.

ved kpl wrote

> For example, filesrc sends bytes from 150 to 200 in the first chunk and
> 100-150 in the second chunk.
> Will it mark DISCONT the second chunk?

   i guess  you meant 100-149.
   should not, since the 150-200 is continuous w.r.t 100-149.

Yes, you're right, thanks.

ved kpl wrote

> Going further, to the MPEG demuxer, processing a video file with I, P and B
> frames. How are they marked?
   GST_BUFFER_FLAG_DELTA_UNIT.
   http://www.gstreamer.net/data/doc/gstreamer/head/gstreamer/html/gstreamer-GstBuffer.html#GstBufferFlag

I meant, in the context of this DISCONT marking.
I am failing to understand in which order the frames will be sent downstream.
And also I cannot completely understand the role of mpegvideoparse mpegpsdemuxer elements.

Probably, you can share with me a knowledge about the flags, that libmpeg2 returns?
Particularly, why are some frames marked with PIC_FLAG_SKIP?