[Matroska-devel] Re: Lossless audio codecs for video editing

David Bryant dbryant at impulse.net
Thu Dec 30 07:53:22 CET 2004

WavPack blocks can contain any number of samples, from 1 to several hundred
thousand (either mono or stereo). If samples are inserted or deleted at a
certain spot in a stream, then only that block needs to be re-encoded; all
others are unaffected.

In a real WavPack stream the block headers would have to be rewritten,
although this goes very quickly. In Matroska the WavPack blocks are being
used in a "raw" mode so I think that no modifications would be needed.

Quoting Christian HJ Wiesner <chris at matroska.org>:

> Hi,
> this email is sent to flac-dev AT xiph DOT org, copied to matroska-devel
> AT lists DOT matroska DOT org, and David Bryant, the author of Wavpack4.
> We are about to implement the DV ( Digital Video ) video compression 
> standard into matroska, to be able to offer an intelligent alternative 
> to AVI for DV handling in editor tools. DV is using a high quality, high
> bitrate lossy video compression similar to MJPEG, so there are no I/P/B 
> frames, you can cut the DV AVI wherever you like. The sound is typically
> PCM, and in a type 1 DV AVI the video and audio will form a single 
> stream ( like in the DV format itself ). As most AVI editors cant handle
> a stream containing  audio and video, there is also type 2 DV AVI, where
> the PCM audio stream is repeated in a second track, to make it 
> accessible. I heard Virtualdub has recently added support for type 1 DV 
> AVI, but i couldnt verify this.
> Our goal is to allow the use of lossless audio with a single DV video ( 
> PCM audio stripped ), to save HDD space during the editing process. MKV 
> has perfect support for FLAC since more than a year, and we are about to
> add Wavpack4 support right now.
> I was wondering how suitable both are with respect to video editing, 
> especially if it comes to sample precise cutting. What is the absolute 
> minimal number of samples per frame in a FLAC stream ? Can we change the
> number of samples in the same track ?
> Hopefully you understand where my question is coming from, we normally 
> cant cut audio streams in between frames during the video editing 
> process, but its not given in any case that frame boundaries of the DV 
> video stream will match those of the audio stream, and this could lead 
> to problems. For this reason we will concentrate on the one lossless 
> audio format for the DV editing that will allow us the finest sample 
> size, for precise editing.
> I know we could try to dig this all up from your docs, but maybe you 
> have an idea how we could best use your codecs for this purpose ?
> Christian
> matroska project admin
> http://www.matroska.org

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