[FFmpeg-devel] Ticket4753 question

[Ganesh Ajjanagadde]

On Fri, Aug 7, 2015 at 6:05 PM, Paul B Mahol <onemda at gmail.com> wrote:
> Dana 7. 8. 2015. 22:44 osoba "Ganesh Ajjanagadde" <gajjanag at mit.edu>
> napisala je:
>>
>> On Fri, Aug 7, 2015 at 4:09 PM, Paul B Mahol <onemda at gmail.com> wrote:
>> > On 8/7/15, Ganesh Ajjanagadde <gajjanag at mit.edu> wrote:
>> >> On Fri, Aug 7, 2015 at 11:59 AM, Paul B Mahol <onemda at gmail.com> wrote:
>> >>> On 8/7/15, Ganesh Ajjanagadde <gajjanag at mit.edu> wrote:
>> >>>> https://trac.ffmpeg.org/ticket/4753:
>> >>>> The issue seems to come from the fact that there are multiple frames
> per
>> >>>> packet.
>> >>>> In fact, the duration field of the packet is set incorrectly,
>> >>>> and reports the duration of a single frame only (80).
>> >>>> Unfortunately, I do not know about where/how this needs to be done,
>> >>>> but can do this if a dev outlines the process.
>> >>>
>> >>> Write trivial g729_parser which splits input into 8 byte packets.
>> >>
>> >> Thanks, I have implemented the 8 byte case.
>> >>
>> >>>
>> >>> Problem is how to tell parser from demuxer that another non 8 byte
>> >>> mode is in operation.
>> >>> Because decoder operates in one of two modes, either 8 byte or 10
> byte.
>> >>
>> >> This is tricky. A dirty but simple solution would be to add a field to
>> >> the priv_data of the avctx,
>> >> i.e to G729Context to represent the format, and use that in the parser.
>> >> I have not seen any other parser do this though.
>> >>
>> >> Note that the parser is quite limited in what it can see:
>> >> the AVCodecParserContext can't contain this information as far as I can
>> >> tell,
>> >> so only AVCodecContext can.
>> >> In this case I don't know how to do this without resorting to the
> priv_data.
>> >
>> > At decoder level you can not guess it, neither at demuxer level and
>> > AFAIK only wav does
>> > put multiple frames into single packet. The only way is via option but
>> > AFAIK you can not read decoder options from parser.
>>
>> I must be missing something, g729dec.c decode_frame does set packet_type
>> to the appropriate mode based on avpkt->size.
>> In fact, this is how currently the two modes (8k vs 6.4k) are
> differentiated.
>> Why can't this be used to set a flag in avctx->priv_data (barring the
> ugliness)?
>
> For example 80 is multiple of 8 and 10 you can't use that to guess mode.

True, but that is a general failing of the decoder currently present.
By setting the priv_data,
we are making as good an effort as the decoder currently does.

>>
>> >
>> >>
>> >> Any suggestions?
>> >>
>> >>>
>> >>>>
>> >>>> Thanks,
>> >>>> Ganesh
>> >>>> _______________________________________________
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>> >>>>
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