Is Hi-definition MPEG2 encoding using ffmmegx possible?

[didier]

Hi,
Can anyone please tell me if I can take a 1280*720 Pixlet encoded Quicktime Movie and encode it to an MPEG2 1280*720 file (Program or Transport Stream) using ffmpegx? Does it support movies of this size?
Someone told me of a plugin that enables this, but reading the docs it looks like it might be supported normally.

Many thanks

[qshartle]

why do you need a hd mpeg2 file?




Q

Because I'm editing HD footage on the Mac and would like to archive back to DVHS, I was hoping this utility might encode HD res MPEG2 from an HD res .mov file. Can it?

[major]

It should work with mpeg-1.

[BJ_M]

It should work with mpeg-1.

HD mpeg2 is Main Profile , High level Profile ID for 720p and 1080i and 1080p (can you set in ffmpegx?)

mpeg1 doesnt use profiles but since you can encode up to 4000x4000 in mpeg1 -- should be no issues (except must be multiple of 16 and progressive)

It has to be Mpeg2, as DVHS only accepts MPEG2 format, (MPEG2 Transport streamto be exact, but I can convert to Transport Stream from Program Stream using the Womble editor on the PC if necessary.)
I don't understand what this "High Profile" thing means I'm afraid.

Thanks for your help.

[BJ_M]

Womble will not correctly convert a HD program stream to a transport stream im afraid .. the multiplexer I use is ungodly expensive for HD transport streams (manzanita) but i dont know of to many others (so i can say its the best) ..

the main concept encoder on the pc can encode to HD and create a transport stream with mpeg audio (or null stream audio) - you may have to go this route. It is a cheaper option (and produces excellent quality) ...

without setting High Profile, the mpeg2 stream is limited in resolution to basicly dvd ... there are even higher profiles for greater than HD resolutions , as well as multiple angle profiles and 4:2:2 profiles (and others)...

[BJ_M]

the correct way edit HD is to use a proxy file anyway as FCP with or with hardware assist is to slow .(same goes for film editing) , its not apples fault -- these are just big files and require a lot of power and bandwidth ...

what you do is encode a smaller file as dv or quicktime (720 x 480) but same frame rate and edit that file ... when your done -- you either replace the source with the same settings or conform -- fcp can do this quite well in fact ...

Sorry, but I don't understand what this "Setting High Profile" means. I do know that the latest version of Womble will definately convert an HD res Program Stream to a Transport stream though, as I have it and know of several people that are doing that. From a non-techie point of view, you would think that it wouldn't require much of a code change in ffmpeg to enable higher resolution encoding, if it uses the same compression scheme. The cheapest HD MPEG2 encoder on the Mac is from Heuris at around $5,000 I believe, which the average joe like myself is definately not going to pay.

With regard to offline HD editing, yes I've used the proxy process, but as of this week you can edit HD in native 720p format on the Mac without additional hardware, using the new Pixlet codec. I know because that's what I'm doing, it's much better than using a proxy, but for archiving I'd like to be able to convert to MPEG2 and output to DVHS, which is why I'm interested in ffmpegx.

Thanks

[BJ_M]

well if it works for you -- go for it (conversion in womble) , but ive checked its output with M-Probe and it is not a valid transport stream .. but I guess it is "good enough" to get by ...

ill check out that Pixlet codec, thanks , though i work on SGI and pc most of the time .. im always interisted in apple stuff ..


i see (http://www.filmmaker.com/article382.html) , its a wavlet codec like i use on QuVis .... you convert your film into this format for editing -- almost just like a proxy except in native res..

Definately good enough for not only previewing HD rough cuts, but they designed it so you could edit with it (HD on a Powerbook?). The fact that it is 48-bit colour means it will probably be suitable for some colour correction work. We will have to wait an see how the compression works. Output on a monitor will depend on third-party support from various video board companies. Again, we probably won’t know more till it is released. You should however be able to use it with the S-Video out on the G5’s (with Apple DVI-to-video adaptor). The codec is scaleable, so it will work with standard definition and should even work with 2K (which is why Pixar want it).

well now it is released -- guess i should upgrade to QT 6.4

Thank you for the feedback, so is the answer to my question about encoding HD res MPEG2 in ffmpegx a definite No?
If so, how hard do you think it would be to change the code to handle Hi-def resolutions (720p in particular)?

Cheers

[qshartle]

I wondering, what is so special about DVHS?




Q

[BJ_M]

well im a sucker for punishment -- i downloaded all the source code used in FFmpegX relating to mpeg encoding and using the FFmpeg component of FFmpegX , no (does do transport stream though - but max resolution is PAL DVD)

but -

mpeg2enc - YES !

you (or someone) will have set the following:



set to 4

/* Level ID */ 

Specifies coded parameter constraints, such as bitrate, sample rate, and maximum allowed motion vector range. 

Code Meaning Typical use ---- --------------- ----------------------------------------------- 4 High Level HDTV production rates: e.g. 1920 x 1080 x 30 Hz 6 High 1440 Level HDTV consumer rates: e.g. 1440 x 960 x 30 Hz 8 Main Level CCIR 601 rates: e.g. 720 x 480 x 30 Hz 10 Low Level SIF video rate: e.g. 352 x 240 x 30 Hz

set to 512 (for 19.2meg/s standard 720p)

/* vbv_buffer_size (in multiples 16 kbit) */ 

Specifies, according to the Video Buffering Verifier decoder model, the size of the bitstream input buffer required in downstream decoders in order for the sequence to be decoded without underflows or or overflows. You probably will wish to leave this value at 112 for MPEG-2 Main Profile at Main Level, and 20 for Constrained Parameters Bitstreams MPEG-1.

set to 2 for DC_P

/* intra_dc_precision */ 

Specifies the effective precision of the DC coefficient in MPEG-2 intra coded macroblocks. 10-bits usually achieves quality saturation. 

Code Meaning ---- ----------------- 0 8 bit 1 9 bit 2 10 bit 3 11 bit

set to all 24's (or 32's) except for position 1 which must be a 8 (you will need to build a table they explain (simple))

/* name of intra quant matrix file ("-": default matrix) */ 

Setting this to a value other than - specifies a file containing a custom intra quantization matrix to be used instead of the default matrix specified in ISO/IEC 13818-2 and 11172-2. This file has to contain 64 integer values (range 1...255) separated by white space (blank, tab, or newline), one corresponding to each of the 64 DCT coefficients. They are ordered line by line, i.e. v-u frequency matrix order (not by the zig-zag pattern used for transmission). The file intra.mat contains the default matrix as a starting point for customization. It is neither necessary or recommended to specify the default matrix explicitly. 

Large values correspond to coarse quantization and consequently more noise at that particular spatial frequency. 

For the intra quantization matrix, the first value in the file (DC value) is ignored. Use the parameter intra_dc_precision (see below) to define the quantization of the DC value.

use default (all 16's):

/* name of non intra quant matrix file ("-": default matrix) */ 

This parameter field follows the same rules as described for the above intra quant matrix parameter, but specifies the file for the NON-INTRA coded (predicted / interpolated) blocks. In this case the first coefficient of the matrix is NOT ignored. 

The default matrix uses a constant value of 16 for all 64 coefficients. (a flat matrix is thought to statistically minimize mean square error). The file inter.mat contains an alternate matrix, used in the MPEG-2 test model.

Wow! So just to make sure I'm not dreaming, are you saying that if I download the source code for mpeg2enc and change these four variables (or tables), then re-compile it, that it will then be able to encode an 720p MPEG2 program stream (or transport stream not sure which you mean)???
If so I think I owe you a Christmas present!!

Thanks

[BJ_M]

Wow! So just to make sure I'm not dreaming, are you saying that if I download the source code for mpeg2enc and change these four variables (or tables), then re-compile it, that it will then be able to encode an 720p MPEG2 program stream (or transport stream not sure which you mean)???
If so I think I owe you a Christmas present!!

Thanks

yes --- but it will be an elementary stream , you would just have to multiplex it to a program (or transport) stream with the multiplexer of your choice ..

those are the variables required to do 720p (plus of course setting the resolution OF 1024x720 , the bit rate you want, zigzag encoding, progressive frame, 24fps and 16:9 DAR -- all of which i didnt mention in the above post as they are rather self evident) ..

i do a LOT of HD encoding and editing -- why i was intersted (not that i need to use mpeg2enc to do it).

Well what can I say, thank you very very much for taking the time to look into this. If this works it will solve a very big problem for people on the Mac who want to work with footage from the new consumer JVC HD1OU camera but can't, as they can't get the footage back to MPEG2 and DVHS once they've editied it in Pixlet or as uncompressed video.
I haven't programmed for a few years now , but if I can figure ow to get the C compiler going on the Mac I am going to try this out ASAP. I'll let you know how it goes Have you any idea how the quality might compare to any of the commercial MPEG encoders?

Many thanks again.

[BJ_M]

MANY commercial encoders are based on the same basic root (this one) , but are heavly tweaked ... you would have to play around with motion vector settings , pixel movement and such (some of which you can do with that one) .. for your information (ive tested it) the heuris $5000 encoder produces no better results ($60 tmpgenc does a equal or better job for HD).

but you will find your encoding slow - as there are no cpu optimizations in mpeg2enc.

good news is that for a high data rate 720p file .... you really cant get bad results ... it will look good .... you can get slightly better and faster and tigher color control with other encoders -- but you will be very happy with the results you can get with mpeg2enc ...

maybe major could incorporate the HD encoding into FFmpegX ....

that would certainly be something !

[BJ_M]

btw -- i should mention -- there have been MANY reports of problems with QT 6.4 (mac and PC) .. the forums at boris beta , DMM , CC, FM are filled with complaints and problems ..

i should expect to see a new version out fairly soon ...

Thank you, yes I've seen all the stuff on firewire 800 drives getting trashed, pretty nasty. I'm not having any problems with Panther though, and Pixlet runs very smoothly on a dual G5.
Maybe I'll use this little project as a route to getting me back into programming a bit.
On Tmpgenc, are you saying that right out of the box, this $60 shareware utility will encode HD MPEG2 720p?

I'll try not to bug you with any more questions on this, but could you please point me to where the source code is for mpeg2enc? I am hoping I can just recompile that one utility, though maybe it's not as simple as that.

All the best

[BJ_M]

yes -- out of the box, the 60$ tmpgenc encoder will encode HD -and do a darn (very good) good job of it ...


the mpeg streams contain data on which encoder has been used and ive checked with m-probe and some major name places are using it -- i use also at times ..

i am on a new system here at home i just built -so i lost all my history ...

i found the source code on google --it should also be linked through the mpeg.org and major must have it also (may be at sourceforge also)