Practical Implications of Pre-Defined mp4 Level Profiles?

[RacePhan60]

Hi folks,

I'm not a deep video hacker, just a race fan who wants to convert a 10+ year race tape collection to efficient avi/mp4/mp3's...with some likelyhood of being compatible with the new (or soon to be released) crop of standalone DVD/mp4 players...

The objective of this post is to understand the relationship between the proposed "standard" mp4 Level Profiles (as implemented in XviD) and the capture pixel resolution that I want to encode...and perhaps gain some insight into the compatibility lilyhood with standalone players?

Background
I put up a post in the capture forum that explains my capture objectives, equipment and current process:
http://forum.doom9.org/showthread.php?s=&postid=462421
I've also read a bit about the hardware encoders...
I found this link to the mp4 "Level Profiles Definitions":
http://www.m4if.org/resources/profiles/index.php
* Found it in this XviD discussion thread:
http://forum.doom9.org/showthread.php?s=&threadid=53632

Specific Question(s)/Issue(s)
My raw capture is at NTSC (640x480x29.97)...
This is not efficient to encode...especially for my old noisy VHS sources
1/2 NTSC has been proposed in some of the capture guides, but for auto-racing, too much detail (especially the on-screen stats text) is lost.
I tried 3/4 NTSC (480x360) and was pretty happy with the resolution and the encode...
After reading the Level Profiles definition doccumentation, it seemed that having the screen resolution as mod16 might be important. Is it? :confused:
The Advanced Simple L4 (AS L4) is defined for 352x576 max...if I use 448x336 or 512x384 (the mod16's either side of 3/4 NTSC) with AS L4, am I likely to be compliant with the stand-alone encoders? :confused: :confused:


Much Thanks,
RacePhan60:confused:

[RadicalEd]

Mod 16 matters for chroma blocks and motion comp. My advice is to crop down from 480x360 to 480x352, if it won't lose too much screen information. That way you're retaining AR, resolution, and divisibility.
The resolution suggested for AS@L4 is just suggested, the real restriction is the macroblock count (this applies to all levels except SP@L0, where the frame size is limited to 176x144). With AS@L4 you have 792 MBs to work with, so 480x352, 448x336, and 512x384 will all work. However, XviD can't yet control the VBV and other level-sensitive values, so the only benefit to following the resolution restrictions and using one of the levels in XviD is that it will be written as compliant with L4, and will work on lenient players or players without level restriction :|

[RacePhan60]

Mod 16 matters for chroma blocks and motion comp. My advice is to crop down from 480x360 to 480x352, if it won't lose too much screen information. That way you're retaining AR, resolution, and divisibility.

OK... I appreciate the response, but it leaves me a bit confused? Is there some specific reason why you suggest I crop instead of just going up or down a step (to 448x336 or 512x384)? My strategy was that if the race was particulary long, I might go down a step to have slightly less overall pixels to compress and otherwise go up and get a little more resolution... If that's a bad approach, I'd like to understand it.


With AS@L4 you have 792 MBs to work with, so 480x352, 448x336, and 512x384 will all work. However, XviD can't yet control the VBV and other level-sensitive values, so the only benefit to following the resolution restrictions and using one of the levels in XviD is that it will be written as compliant with L4, and will work on lenient players or players without level restriction :|


It probably won't help me to know, but what's a VBV?:confused:

I searched the forums and most references seemed to indicate that XviD level profiles primarilly set a flag saying that the file is "compliant," but that some particular characteristics of the file are likely to be non-compliant with the requirements of the indicated level...yep, I think I just managed to say with a whole bunch o'words what you said sucinctly above!:o

So let me try another approach...I have done some searching in the hardware forums, but it was hard to draw conclusions...maybe you have an opinion from feedback and general involvement in this scene...

If I encode with L4 profile (using any of the resolutions discussed above), would a standalone player (say one based on a MT1389xx chipset), be likely to play it?

Seems things to look out for are, too high bit rate, they don't appear to like B-frames(?)...what other settings/parameters might I not want to use or use to improve my chances of compatibility?

Thanks for your patience and help,
RacePhan60