[FFmpeg-user] considering image sequence+audio for video preservation

[Kieran O Leary]

Hi,

On Sun, Jun 12, 2016 at 11:58 AM, ibrahim <ibrahim at httpdot.net> wrote:
> hi,
>
>FFV1+lpcm+mkv is a perfect solution that meets
> most of the preservation requirements for video and i would recommend
> that as the first option but i am also working on an additional strategy
> based on keeping the video as image sequence+audio, which would make the
> video part independent of video codecs and the multimedia containers.

I work in a film/tape archive and we are going to use FFV1.mkv where
we can. As I'm sure you've discovered, many archives are starting to
do the same. This upcoming symposium in July could be of interest to
you: https://mediaarea.net/MediaConch/notimetowait.html

>i am posting this to ffmpeg user
> list since I believe ffmpeg is the best platform to carry such activity
> of having control over the process of transcoding a video to image
> sequence + audio but any recommendation to post this to another list as
> well is also welcome.
>

The AMIA listserv might be of use to you and there might be questions
like this already asked in their archives:
http://www.amianet.org/participate/listserv.php

> the image format for the image sequence should be a lossless compressed
> or uncompressed free/libre format and it should preserve the significant
> properties of video such as interlacing, colour space (without any
> colour conversion), chroma subsampling and bitdepth.  I know that no
> such image format exists. png is my best option but:
> -png is up to 8bpc (besides alpha) RGB. besides YUV to RGB colour space
> conversion, i will loose information for 10 bpc formats such as prores
> 4:2:2 when represented as 8bpc. Is there a free/libre lossless image
> format that can handle greater bitdepths? since all displays are RGB, a
> color conversion to RGB is eventually mandatory, at least when
> displaying the video/image. does anybody have a prediction that the
> display technology will switch to anything other than RGB? and my
> approach is that it would be ok to transcode to an RGB image format
> since more video codecs are expected to be RGB sometime in the future
> and the RGB image sequence can be transcoded to a RGB video format for
> access, and even for migrating to another preservation format without
> further color space conversion. what do you think? how justifiable is
> this approach?

Are you saying that you would use an RGB still image format for your
YUV videos because YUV decodes to RGB anyhow? It would seem to me that
one of the significant properties of your source is the colour space,
and altering it for your long term preservation file seems a bit risky
and unnecessary?

>How good ffmpeg handle color space conversion for png
> image sequence? Are there any free/libre image format to preserve
> original YUV color space, original chroma subsampling and bitdepth? The
> file size is not a constraint but being a free/libre format is...
> -can PNG handle original interlacing? If one exports a png image
> sequence from an interlaced video using ffmpeg, can it be later imported
> back as an interlaced image sequence preserving original interlacing? If
> PNG cannot handle original video interlacing, are there any other
> free/libre image formats that can?

As it seems to be an SMPTE standard, it probably isn't free/libre, but
have you investigated DPX? I know very little about it for
YUV/Interlacement, but I think it might support some of your needs. It
seems to have some support for broadcast.
http://www.digitalpreservation.gov/formats/fdd/fdd000178.shtml .
However, I think your ffv1/lcpm/mkv approach is a much better option.

If FFV1 supported log values, I would transcode our film image
sequences into FFV1, which is the exact opposite of what you are
researching.

FLIF is something I've heard a few things about, but I don't think
ffmpeg supports it.http://flif.info/ I think it might have been based
on, or at least inspired  by FFV1? It doesn't seem to support YUV
values, but perhaps you could get in touch with the developer as the
format is still evolving. However, I think it's probably best to leave
your moving image video files as moving image video files, and not
convert them to image sequences!

I wish you the best with your research and I'd love to know how you get on.

Best,

Kieran.