[FFmpeg-devel] [RFC] be more kind with wrong psm in mpeg ps

Baptiste Coudurier baptiste.coudurier
Mon Apr 21 11:02:55 CEST 2008

Baptiste Coudurier wrote:
> Hi,
> M?ns Rullg?rd wrote:
>> Michael Niedermayer wrote:
>>> On Mon, Apr 07, 2008 at 04:36:41PM +0200, Baptiste Coudurier wrote:
>>>> M?ns Rullg?rd wrote:
>>>>> Baptiste Coudurier wrote:
>>>>>> Hi,
>>>>>> Attached patch make ps demuxer correctly detects lpcm files with wrong
>>>>>> psm (mplayer and vlc plays them correctly).
>>>>>> Should fix wrong_psm_lpcm.mpg on mplayerhq.
>>>>>> I think those checks are reasonable. Comments ?
>>>>> I don't like it.  It can break valid files.
>>>> Question is does it ?
>>>> I'd like some real measures of the effects of the psm considering vlc
>>>> and mplayer ignore it and play many files.
>>>> if psm says AC3 or DTS then fine, but if psm says private data or mpeg1
>>>> audio, it's reasonable to guess that it is not what psm says.
>>>> I think I'll ask for a vote on this, since I would really like being
>>>> able to play those files.
>>> I am in favor of having as many files as possible supported. So if this patch
>>> makes files playable that arent currently and we have none that it breaks
>>> then, iam in favor of the patch.
>>> Maybe a compromise would be printing a "This file specifies an invalid codec
>>> in the PSM"?
>>> Also without checking the spec, what is invalid if a AC3/DTS/MP3/LPCM is
>>> "private data"? IMHO if something else indicates a more specific type that
>>> should override "private data". But maybe i misunderstood something?
>> If the PSM says private data (stream_type == 6), there is no telling what
>> it is, unless some descriptor or other identifies it.  AC3, DTS, and PCM
>> are not supported by the ISO spec at all, and several incompatible
>> extensions to handle these codecs exist, the most common being that found
>> on DVDs.
> Atm, if psm says private data, track is just ignored by lavf, however,
> if track uses dvd private data mechanism, it is IMHO easy to support it.
> Do we need a vote for this ? I'd really like lavf to support those files 
> like mplayer and vlc do.


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