[FFmpeg-devel] ffmpeg mpegts muxing overhead

[Pushkar Pradhan]

Hi Coudurier,

On Tue, Jan 18, 2011 at 11:14 AM, Baptiste Coudurier <
baptiste.coudurier at gmail.com> wrote:

> Hi
>
>
> On 01/18/2011 09:05 AM, Pushkar Pradhan wrote:
>
>> On Mon, Jan 17, 2011 at 11:38 PM, Tomas H?rdin<tomas.hardin at codemill.se
>> >wrote:
>>
>>  Pushkar Pradhan skrev 2011-01-18 01:39:
>>>
>>>  I need to be able to predict the mpegts muxing overhead before the
>>> actual
>>>
>>>> muxing happens.
>>>>
>>>>  Why? Also, does it need to be exact, or can it be an overestimate?
>>>
>>
>> This is for HTTP Live Streaming. We need to publish the bitrate in the
>> playlist. If the actual bitrate deviates too much (20-25%) from the
>> published the App Store rejects the app. In our architecture the playlist
>> has to be sent out before doing the actual muxing. Otherwise it is a big
>> architectural change. So the estimate has to be within a reasonable limit.
>>
>
> You can specify a muxrate to the muxer which will add padding as necessary.
> Account video bitrate + audio bitrate + reasonable margin.
>
I think you're talking about the AVFormatContext:mux_rate which is used as
the MpegTSWrite muxrate, the default is 1. I followed this variable's use in
mpegtsenc.c and found that it is used to set the pcr values written out. It
also inserts null packets or pcr_only packets if some other conditions on
the DTS are also satisfied.
So overall, I see it will increase the muxing overhead, but not make it a
fixed size.
I think most of the muxing overhead comes from padding the TS packets when
writing out the PES packet. IMHO this cannot be predicted unless you know
the frame sizes etc.

Or am I missing something?


> --
> Baptiste COUDURIER
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-- 
pushkar