Photo-JPEG MOV Files Show As MJPEG
A unified display of relevant technical and tag data for A/V files
Brought to you by:
guillaumeroques,
zenitram
I don't see any bug in this:
- M-JPEG is multiple JPEG image stream, each JPEG imagine is independant, but displayed 1 per 1 at a specified frame rate
- Photo-CD (Photo-JPEG) are multiple JPEG image stream, each JPEG imagine is independant, but displayed 1 per 1 at a specified frame rate
What should be displayed from your point of view? On my side, I don't see any technical difference.
[Begin Quote]
So just for the record, here's some useful and reliable info:
JPEG is a lossy format, and there are 2 main sources of loss when a JPEG
codec is used- firstly there's chroma downsampling and secondly there's
quantisation. There are also some small rounding errors which result
from the overall process but they are negligible.
The most significant piece of information to know is that at 100%
quality, all 3 codecs do not downsample chroma (they work at 4:4:4) and
they do not quantise the resulting data (they use a quantisation table
of 1s). At 100% quality the only losses come from rounding errors and
these are negligible.
In other words, at 100% quality Photo JPEG, MJPEGA & MJPEGB are all
practically lossless.
There are some important differences between the codecs, however.
Both the MJPEG codecs allow fields and a field order to be specified,
and if used the fields are compressed separately and then combined. This
prevents artifacts from mushing fields together, and at lower quality
settings this can make a significant difference. For this reason alone,
anyone working with interlaced video should use the MJPEG codecs and not
the Photo JPEG codec.
At quality levels below 100%, chroma is downsampled respective to the
quality level selected, but Photo JPEG samples at 4:2:0 (ie. vertical
samples) while the MJPEG codecs sample at 4:2:2 (ie. horizontal
samples). In terms of video footage, this relates to a fields issue and is another
reason why you should use MJPEG codecs for interlaced footage instead of
Photo JPEG. If your video footage is frames (eg. footage shot on film
and telecined 1:1) then it's less of an issue.
As has been pointed out before, there is no quality difference between
MJPEGA and MJPEGB, they are simply optimized for different hardware
decoders.
In summary- at 100% quality all 3 codecs are practically lossless.
Below 100%, the fact that the MJPEG codecs compress fields separately and
downsample chroma horizontally means they will deliver better quality
results from interlaced footage. Photo JPEG does not compress fields
separately and downsamples chroma vertically, which can lead to field
mush when used with interlaced footage.
[End Quote]
So although the differences are subtle, an editor needs to know which of the codecs is in use, especially when cutting stock footage in the same timeline with camera footage.
-Jeff
OK, I understand better now.
So now, I need a sample, to see what is the difference in the codec identifier between M-JPEG and Photo-JPEG. I hope there are any!
Please provide a sample, I can provide a private FTP server access for upload if you need it.
Or more useful is the CodecID (in the text view).
At home, I have thess CodecIDs:
jpeg (there is a "compressor name" = "Photo -JPEG", so I imagine you think about this one)
MJPG
mjpa (I imagine this is M-JPEG A)
I think I will not change the name of the format, but add a "profile ("A", "B", "Photo").
I don't provide yet lot of info about M-JPEG, I will try to add this (Chroma, Interlacement...)
I believe that the FOURCC code for Photo-JPEG is simply JPEG.
Here's the link to the sample file:
http://bellunevideo.com/client1/ACB101.mov
Thanks,
-Jeff