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Old July 11th 18, 12:07 AM posted to alt.windows7.general,microsoft.public.windowsxp.general,microsoft.public.win98.gen_discussion,uk.tech.broadcast
Paul[_6_]
external usenet poster
 
Posts: 41
Default Does .mp4 - or any other video format - have a text field (comment,not subtitle)? If so, what can edit it?

J. P. Gilliver (John) wrote:
In message , R.Wieser
writes:
John,

_is_ there something intrinsic to the format?


The specs to the format seem to indicate there is, and I found
something to
manipulate it here :

https://community.wd.com/t/how-do-yo...kv-and-mp4-fil
es/169392

VLC does it for some video files, using something that was/is so obvious
I hadn't spotted it (-:
[]
Personally I would not depend on those ADSes, but wanted to name them
regardless. - both as an option, but also as a warning :-)


I don't want to use something associated by the filesystem; that's not
that different, to me, from storing a text file of the same name in the
folder. I wanted something that actually makes the comment part of the
file, like IrfanView (and maybe others?) does with .jpg comments: so
that they'd even survive being emailed, for example. (Not that I'd often
email video files, I just give that as an example.)

Regards,
Rudy Wieser

P.s.
Had to remove "uk.tech.broadcast". Its not carried by my usenet server.

Interesting; I don't think any of the servers I use (with the possible
exception of the Mozilla one) object to such headers. My news _software_
fails if I try to post something where _none_ of the 'groups specified
are carried by any of the servers, but not where only some of them
aren't. (It doesn't _tell_ me it's failing - just the post sits in the
outbox for ever, doesn't go. [It _does_ object if I use a newsgroup it
knows is carried by _none_ of the servers it deals with, as I just
rediscovered as I'd mistyped UTB.]) Note I've added UTB back in case
anyone there is following.


Just a couple quick notes.

1) The file extension might be used to signify the "container".
.mkv, .avi, .mp4 might be containers.

The reference section at the bottom, has a list of containers.
The Apple MOV container, became the prototype of one of the
newer standard container.

https://en.wikipedia.org/wiki/.mkv

The "container" can contain multiple kinds of "codecs"
for audio and video. For example, .wtv files from Windows Media Center,
basically just record off the DVB you're getting, and keep
five audio and video streams in the same file. This then
requires a "selector" to select the desired stream, on
"dumb" players. This command selects stream 2,3 from the five available.

ffplay -ast 2 -vst 3 -x 704 -y 480 some.wtv

In some cases, when a container has only audio in it,
the file extension changes (to help "home collectors").
Maybe that would be .m4a or the like.

2) Whether they're images or video, formats which use packets
and the packet header uses a 4CC (four character code), those allow
out of band material to be added.

video_packet video_packet audio_packet video_packet

video_packet video_packet comment audio_packet video_packet

The idea is, the parser playing the movie, reads the packets
with the identifiers it understands (video,audio), and ignores
any other comment. This allows EXIF and XMP to be injected
into the same file, as they could just be packets.

3) Formats that are not packetized, may still offer opportunities
for the addition of metadata, but due to a lack of standards for
that, it's not very useful. A text PPM file for example, is text inside,
and any line beginning with "#" is a comment. A comment where
you could hide some necessary info. Don't expect any tool flow
or Windows Search to honor such a feature.

There are a few tools that are useful.

1) GSpot for CODEC identification within the container.
2) HxD hex editor, if you really want to examine the file format.
3) EXIFTool, if studying EXIF data.
4) FFProbe (a part of FFMPEG) can convert the packets
into individually delimited pages in a "dump". You can
see the interleaved video and audio pattern. The IPB frames.
And FFProbe would also identify the CODECs present.
(A good choice, since FFMPEG is kept up-to-date.
GSpot development stopped some time ago.)

Windows Search only has search providers for a limited set
of EXIF types. For example

ext:jpg AND camera:Nikon

might dig up all the JPG files photographed with a Nikon
camera. You can actually dump the windows.esb (esedb) and
find out what kind of fields are in it. (That's if you don't
trust the latest web documentation for how the search works.)
Peter is the person who most often asks questions about
this aspect. He must be an expert by now.

Paul