[Matroska-devel] Fwd: WebM file validation tool

Christian Wiesner cwiesner at matroska.org
Mon May 24 11:30:49 CEST 2010


Is this really clever ?

Why can't we leave matroska as it is, and have a WebM subset of matroska ?

Christian


2010/5/24 Steve Lhomme <slhomme at matroska.org>

> A lot of discussions are happening on the WebM mailing list.
> This one may end up removing TrackTimecodeScale from Matroska (or simply
> mark it as deprecated).
>
> ---------- Forwarded message ----------
> From: Steve Lhomme <slhomme at matroska.org>
> Date: Mon, May 24, 2010 at 9:24 AM
> Subject: Re: WebM file validation tool
> To: Frank Galligan <fgalligan at google.com>
> Cc: j <j at v2v.cc>, WebM Discussion <webm-discuss at webmproject.org>
>
>
> Also the explanation seem bogus. The Cluster timecode should not be scaled
> by the track, otherwise that means that data from 2 tracks don't have the
> same time base to be muxed in the same Cluster. Given there are as many
> possible ways as there are channels the resulting muxing will end up being
> suboptimal for only 1 track combination. For the others, the audio
> corresponding to a video channel may end up being in a another Cluster,
> maybe even many Clusters away if the stream is long enough. That's terrible
> for playback.
>
> Wether the TrackTimecodeScale is applied during playback or during muxing,
> the problem is still there. After some time the actual audio timecode may be
> too far from the video data and b0rk the player caching resulting in jerky
> or loss of playback. So in the end the TrackTimecodeScale is a bad solution
> to a tricky (and rare) problem.
>
>
> On Mon, May 24, 2010 at 8:59 AM, Steve Lhomme <slhomme at matroska.org>wrote:
>
>> Hi Frank,
>>
>> A lot of Matroska readers/players can read and handle the value. But I
>> don't know any program that can output something else than 1.0 (the default
>> value). The only program that may have is mkvmerge, but I checked the code
>> and it doesn't. So dropping the element, even player side, could be fine. At
>> worse those file where it's written it can be discarded.
>>
>> The reason for TrackTimecodeScale to exist is described here:
>> http://www.matroska.org/technical/specs/notes.html#TrackTimecodeScale
>>
>> <http://www.matroska.org/technical/specs/notes.html#TrackTimecodeScale>It
>> was designed when you could get the video from a framerate and then the
>> audio from another source (in another language) and you try to mux them
>> together without reencoding. Technically it's always possible to adjust the
>> video framerate to match the audio (although it won't look natural). It
>> becomes impossible when you merge more than 1 "heterogeneous" source
>> together.
>>
>> This is a very corner case, so much that it's not in use anywhere, and may
>> likely never be used. The only use is when the encoded audio doesn't get
>> reencoded. So maybe it can be useful for storage of a "Master", but that's
>> it.
>>
>> On Mon, May 24, 2010 at 3:25 AM, Frank Galligan <fgalligan at google.com>wrote:
>>
>>> Steve,
>>>
>>> Do you know if any Matroska implementations use TrackTimecodeScale? I
>>> would like to submit a patch to FFmpeg but they would like to use as much of
>>> the same code for Webm and Matroska.
>>>
>>> Frank
>>>
>>>
>>> On Sat, May 22, 2010 at 12:06 PM, Steve Lhomme <slhomme at matroska.org>wrote:
>>>
>>>> On Sat, May 22, 2010 at 6:03 PM, <j at v2v.cc> wrote:
>>>>
>>>>>  > Yup, it's called mkvalidator:
>>>>> > http://www.matroska.org/downloads/mkvalidator.html
>>>>> >
>>>>> > It was broken with "live streams" but I fixed it today. I haven't
>>>>> made a
>>>>> > new package though. You can always build it from SVN.
>>>>> >
>>>>>
>>>>> for files created with the latest patches and ffmpeg i get ERR201
>>>>> is this a know problem with the current ffmpeg patches?
>>>>>
>>>>> ERR201: Invalid TrackTimecodeScale for profile 'webm v2' at 386 in
>>>>> TrackEntry
>>>>> ERR201: Invalid TrackTimecodeScale for profile 'webm v2' at 461 in
>>>>> TrackEntry
>>>>>
>>>>
>>>> Yes, TrackTimecodeScale is not part of webm.
>>>>
>>>>
>>>
>>
>
>
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