[MPlayer-users] AVI 2 SVCD

[Nico]

HR wrote:

>>keyint=132 may result in a too long GOP
>>The standard for PAL DVD  is 15, but you might experience a better
>>compression/quality ratio increasing it to some value like 75 
>>(3 seconds,
>>in my experience it's a good compromise, but you should make some test
>>to see how long a GOP your player can handle).
>>    
>>
>Hmm, I did get some (unacceptable) "vibration" in the video with my
>settings - it plays fine on various software players. By vibration, I
>mean the movie sometimes got previous frames repeated in the stream,
>leading to funky "flashbacks" and "vibration" in movements. Can this be
>
I experienced ghosts and color patches with long GOPs and also vertical 
tearing.
DVD standalones are supposed to read 15/18 GOPs movies of near-perfect 
quality,
so you should never rely too much on their  versatility and on their 
ability to apply post-processing.
I guess there's still some bug in the encoder, read below.

>a keyint/GOP problem? Furthermore, I could not seek in the movie with my
>standalone player... any reason for this? The same, perhaps? And I
>didn't use B frames, which I probably should.
>  
>
there are a number of reasons why I never use bframes (based on my 
experience):
1) it seems they are a bit slower to encode than IP only GOPS
2) they don't help quality at all, rather the opposite
3) I read in the ffmpeg-devel that there's a bug in the current version 
of libavcodec
for which bframes are stored incorrectly in the bitstream;

http://sourceforge.net/mailarchive/forum.php?thread_id=3543640&forum_id=1506

not knowing how the mechanism works I can't confirm nor deny it, but to 
play safe ...

In addition I found something strange: encoding to mpeg1/2 I never 
specified any
setting related to bframes, and I assumed (from the man page) that 
vmax_b_frames defaulted
to 0, yet in certain sections of the movie Virtualdub detected 1 B 
before any P,
so I added vmax_b_frames=0 and all was fine.

>What is the exact relationship between keyframes (intra) and GOPs? Does
>keyframes define the boundaries of GOPs, and can/will a GOP contain
>keyframes within?
>  
>
GOPs are sequences of frames, which must begin with an I (keyframe), e.g.
IBBPBBPBBPBBPBB
is the standard sequence for PAL DVDs
so keyframes in this case define GOP boundaries

>  
>
>>lavc's mp2 seems to be far more compatible than ac3, and it 
>>doesn't sound
>>bad at
>>all (at least on the players I tested).
>>    
>>
>By compatible, do you mean "lavc's ac3" or any ac3, given that there to
>my surprise be any difference what-so-ever?
>

lavc's ac3. My player (and others) never played it, so obviously 
something is still wrong
in the bitstream generated by lavc (cvs)

>Anyway, IMHO for non-surround audio, 224kbps mp2 is quite adequate for
>most practical purposes. I would guess you need a good sound setup, good
>ears and be able to switch between sources to really tell any
>significant difference. But there is no reason not to use AC3, since it
>is supported by any decent standalone DVD players, and certainly by any
>decent SW player. It all depends on the source media, I guess, which
>compression/format is "right" or "neccecary".
>  
>
I never had a 6 channels system, so I always satisfactorily used 128 
kb/s mp2 encoded by toolame;
I'm testing ffmp2 at the moment, and it sounds still acceptable at 96 
kb/s, at least for anime.
Maybe it's not enough for ordinary movies.

>  
>
>>I suggest you to remux the mpeg file you get out of  mplayer with
>>dvb-mplex (in package libdvb-0.5.3) that you can find here:
>>www.metzlerbros.de
>>    
>>
>Any particular reason for preferring this over mjpegtools mplex? Any
>reference on this?
>  
>
it's more confortable: it has an embedded demuxer, so you can pass it an 
mpeg file
of any kind, such as a muxed (a+v) stream generated by mplayer, or a DVB 
broadcast,
or separate A/V files. The muxer is still mjpegtools' one.

>HR
>
>  
>
Nico