pb at das-werkstatt.com
Wed Apr 25 22:39:42 CEST 2012
On 04/25/2012 09:58 PM, Laurent Aimar wrote:
> With MPEG codecs (MPEG-1/2, MPEG-4 ASP, MPEG-4 AVC), theses informations
> (aspect ratio, field order and informations to create telecine streams)
> are contained in the bitstream (some at the picture level, some at the
> sequence level). As such, they can be extracted by the decoder and
> provided to the encoder.
> One use case for AR changes is for TV streams. On some TV channels, 16:9
> was used for movies, and 4:3 for somes ads/old reportages.
Yes, for broadcast-, production and web *streams* this makes perfect
sense (MPEG-*, DV, HDV, ...).
Only some "born digital" material should be converted to lossless. With
some, on the other hand I'm not sure if it's a good idea (or necessary)
to transcode to lossless.
This would be like converting a collection of recordings made directly
to MP3 to WAV: There would be no gain, except for a more homogeneous
format collection in the archive. For video the current size
consummation is a major factor for favoring not to do so.
For analog material, AR information, as well as field-order cannot
automatically be detected in a reasonable way. Maybe if it contains WSS
(Widescreen signaling ) information, but I'm not sure if that can be
stored on e.g. (S)VHS tapes.
Some other material which already has a digital source (like DigiBeta)
cannot be recorded without transcoding. So, mid-stream changes like
AR,etc can also not be recorded in order to provide the information
needed if using FFv1.3's in-stream properties.
As you mention TV-Streams:
If they are analog, WSS could be used, but it's questionable whether
recording analog TV is a proper use-case these days, anyway.
I'm not trying to put these in-stream properties down, I'm just a bit
careful about additional features added to FFv1, that might impede
interoperability and increase effort on non-ffmpeg applications in order
to support FFv1 completely.
Thanks for your feedback,
More information about the ffmpeg-devel