[FFmpeg-devel] [PATCH] AVPacket.display_duration

Baptiste Coudurier baptiste.coudurier
Wed Sep 10 19:51:25 CEST 2008

Michael Niedermayer wrote:
> On Mon, Sep 08, 2008 at 07:21:09PM -0700, Baptiste Coudurier wrote:
>> Hi guys,
>> Michael Niedermayer wrote:
>>> On Tue, Sep 09, 2008 at 01:56:29AM +0200, Aurelien Jacobs wrote:
>>>> Michael Niedermayer wrote:
>>>>> On Fri, Sep 05, 2008 at 05:35:13PM +0200, Aurelien Jacobs wrote:
>>>>>> Hi,
>>>>>> For some subtitles track, each AVPacket must carry the display duration
>>>>>> of the contained subtitle.
>>>>>> The attached patch adds a dedicated AVPacket.display_duration field.
>>>>> Iam not against this, but i would like to understand better for which cases
>>>>> it is needed.
>>>>> plain UTF-8 and ASCII ?
>>>> Exactly.
>>>>> If so does mov, avi, asf, ... support plain UTF-8 and ASCII ?
>>>> I don't think so...
>>>>> if yes how do they know the display_duration ?
>>>> The fact that they can't store any display duration just prevent
>>>> them from storing plain text subtitles. At least I think so.
>>>> Another possibility would be to not support any kind of plain text
>>>> subtitles at all in ffmpeg. Demuxers could convert them to SRT,
>>>> which is basically plain text + timing information. But I'm still
>>>> not sure if I really like this solution.
>>> iam fine with adding display_duration to AVPacket, the only minor
>>> dislike i have with this solution is that codecs with very small
>>> packets might see a minor speedloss with added fields. But then
>>> not adding needed fields is no solution, some other solution for
>>> these small packet audio codecs has to be found if it turns out that
>>> the AVPacket handling overhead matters.
>>> So again iam ok with adding display_duration.
>> So Matroska packets will have 3 kinds of duration ? normal, convergence,
>> and display ? Or is display supposed to replace convergence ? Or am I
>> missing something ?
> There would be 3 different kinds of durations, i do not know if matroska will
> set convergence_duration though, probably not.

If matroska does not use convergence_duration, I think it should rename
the field to display_duration, after all convergence_duration was added
for Matroska. IMHO better not having useless fields.

> I also do not know if this is the best solution, the obvious alternative
> to display_duration is to have the matroska demuxer convert the codec
> bitstream to a representation that contains the display_duration.
> It seems that for all subtitle formats such representations exists, ASS as
> well as plain text (SRT).

What about stream copy ? Should the muxer reformat packets too ?

Baptiste COUDURIER                              GnuPG Key Id: 0x5C1ABAAA
Smartjog USA Inc.                                http://www.smartjog.com
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