[ale] questions for the media gurus

[Michael B. Trausch]

On 7/9/2011 8:57 PM, Narahari 'n' Savitha wrote:
> What is .ogg file, is that opensource equivalent of mp3 ?

As mentioned elsewhere in the thread, Ogg is a container specification. 
The container itself can house many different streams, including Vorbis 
audio and Theora video.

> Can iPod/iPhone play .ogg file ?

Probably via an application, but as I do not have one to test with, I 
cannot answer this definitively.

> Can iTunes/Windows Media Player play .ogg file ?

With a codec appropriately installed, yes (in the case of WMP).  iTunes 
on Windows likely has the same answer. No clue about on OS X.

> Can Android phone play .ogg file ?

Yes. In fact, all of the ringtones shipped with Android phones are 
Vorbis audio in an Ogg container.

> Does .ogg file give good compression ?

Typically given the same settings, I have found that in our collection 
of music, an Ogg Vorbis encoded file will be between 8 and 12 percent 
smaller than the equivalent MP3 file.  This is because Ogg Vorbis 
encoders use Variable-Rate Encoding by default, while most MP3 encoders 
do not.  I have not pitted a VBR MP3 against a VBR Vorbis stream, so I 
don't have the end-all answer for that question.

> What is vorbis file, is that opensource equivalent of <what> ?

I think you meant "Theora".  Ogg is the container.  Vorbis is the audio 
stream format that goes with the container specification (though they 
can also house FLAC streams).  Theora is the video stream format that 
goes with the Ogg container specification.

> Can iPod/iPhone play .vorbis file ?

For all files that use the Ogg container, the official file extension is 
.ogg.  Relatively recent convention says that Ogg containers with audio 
only are .ogg and with video are .ogv.  Not everyone adheres to that 
convention.

> Can iTunes/Windows Media Player play .vorbis file ?

Never tested Theora playback on Windows, but I suspect the answer is the 
same for Vorbis.

> Can Android phone play .vorbis file ?

It should be able to, but I haven't tested.

> Does .vorbis file give good compression ?

In all the files I have seen, it seems comparable.

> Can Myth play vorbis files ?

I see no reason why it shouldn't.  Doesn't Myth use the gstreamer 
backend for processing, or another backend like mplayer that does?

> Can I provide the video file and the cue file to the ffmpeg program 
> and make it trim and join the mark-in and mark-out points to produce 
> video without encoding ?

All data is encoded somehow or another.  I am guessing here that you 
mean "without compression".  The answer is "sure" but it won't do you 
much good.  The video provided by your DVR device is going to already be 
compressed, most likely using one of the many different MPEG standards.  
If you modify the video stream (e.g., decompress it, perform whatever 
modifications you will do it, and then re-compress it), then you will 
have lost a "generation" of the video.  It is not dissimilar from the 
"generation loss" that one experiences when they copy a cassette tape to 
another one, and then use the new one to copy to a third, and so forth.  
This is because when you re-compress the stream, more information will 
be lost. (MPEG is a lossy encoding for video, like JPEG is a lossy 
encoding for still photos, like MP3/Theora are lossy encodings for audio 
streams.  FLAC, in case you were wondering, is lossless.)

If you are going to "splice" out the advertisements in an effort to do 
so without decoding and recoding, I'm not 100% certain that will work.  
A large part of MPEG compression depends on the frame that comes before 
it, with only the deltas specified.  I *think* that there are sync 
points in the video stream, but I can't speak to that because I really 
know very little about MPEG video compression.  You would have to do 
some research there, and experiment with a few videos to see what the 
result would be.

     -- Mike