[FFmpeg-devel] Ticket4753 question

[Ganesh Ajjanagadde]

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)?

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