Re: [Libquicktime-devel] FFmpeg plugin resync DNW for out-of-order B-frames after full sync keyframes

[Derek C. <der...@mi...>]

I've revised and tidied up the initial patch to fix bad logic where it
only skips one B-frame when it should be able to skip more than one
until the next non-B-frame.

I think this thread got lost amidst Burkhard's packet index work but
it is still a valid problem regardless of how we 'retrieve the
previous ref sample', 'check the PTS of a sample', 'check if sample is
B-frame'.  Basically, if you have a packet sequence like:

       pos 1155584 pts 0 dts 0 dur 100 sz 56956 FT I key ref
       pos 1212540 pts -200 dts 100 dur 100 sz 1095 FT B
       pos 1213635 pts -100 dts 200 dur 100 sz 35253 FT B

and try to resync to the 3rd frame (PTS -100), the next frame to be
decoded will end up being the 2nd frame (PTS -200).

Once we are happy with the packet index generation, we can go ahead
with simplifying the *bitstream*() function code to use it.  -- Side
note, I've just come across a file that generates "? key" packet index
entries so for now I've had to use the current demux code - I'll debug
and update on the "New Demultiplexing mode" thread later.

On 5 March 2014 09:38, Derek Chow <der...@mi...> wrote:
> (sorry I've switch email client and forgot to send as plain text -
> original message below):
>
> Example with XDCAM file:
>
> (IBBP... bitstream with 'ctts' 2, -1, -1, 2 ...).
> After seeking (or decoding) to frame 2, use
> quicktime_set_video_position() to then seek backwards to frame 1.
> get_bitstream_sync_frame() returns 0.
> decoded_frames_to_discard becomes < 0 despite "// Should not be < 0
> unless the stream is broken."
>
> Please see possible fix attached.
>
> On 4 March 2014 10:10, Derek Chow <der...@mi...> wrote:
>> Example with XDCAM file:
>>
>> (IBBP... bitstream with 'ctts' 2, -1, -1, 2 ...).
>> After seeking (or decoding) to frame 2, use quicktime_set_video_position()
>> to then seek backwards to frame 1.
>> get_bitstream_sync_frame() returns 0.
>> decoded_frames_to_discard becomes < 0 despite "// Should not be < 0 unless
>> the stream is broken."
>>
>> Please see possible fix attached.
>>
>>
>> Derek Chow / C++ Developer
>>
>> der...@mi... / +44(0)7825373230
>>
>> Office +44 (0)207 884 2530
>> 21 Broadwall, London, SE1 9PL, United Kingdom
>> http://www.mirriad.com
>
>
>
> --
>
>
> Derek Chow / C++ Developer
>
> der...@mi... / +44(0)7825373230
>
> Office +44 (0)207 884 2530
> 21 Broadwall, London, SE1 9PL, United Kingdom
> http://www.mirriad.com



-- 


Derek Chow / C++ Developer

der...@mi... / +44(0)7825373230

Office +44 (0)207 884 2530
21 Broadwall, London, SE1 9PL, United Kingdom
http://www.mirriad.com