Comparing Cirrus Logic versus Conexant hardware encoders?

[HerronScott]

All,

I've been using an ADS Technology Instant DVD 2.0 to capture TV shows from my TiVo and have been very happy with the output (no audio/video sync problems and good quality). I purchased a Leadtek PVR2000 which I believe has a Conexant hardware MPEG encoder (versus the Cirrus Logic one used by the ADS) to try and capture directly to the PC and avoid the middle step and have been interested in the differences in the encoded files. I've got both set for CBR at 4000kbps and using Bitrate Viewer, I find that the ADS file has a rock-solid bitrate 3768-3775kbps and the quantization is also a rock-solid 20.02. When I check a file captured by my Leadtek PVR2000 also set for CBR at 4000kbps, its file's bitrate is more variable with values from 3408-4900 and the quantization ranges from 2-10. I do notice that the quantizaion scale is nonlinear on the ADS and linear on the Leadtek and that the scan types are different between the two - alternate versus zigzag. (See below).

I'd like to know if one should give any better quality than the other based on the files specifications. Unfortunately I have no idea what the merits of one quantization scale are. I would think that the ADS's more constant bitrate is a good sign for a file that's supposed to be CBR. Is the Leadtek's file typical for Conexant-based cards like the Hauppage?

Thanks for any information you can give me!


Scott

ADS Instant DVD 2.0 file (Cirrus Logic encoder):

Num. of picture read: 108473
Stream type: MPEG-2 MP@ML VBR
Resolution: 720*480
Aspect ratio: 4:3 Generic
Framerate: 29.97
Nom. bitrate: 3999600 Bit/Sec
VBV buffer size: 112
Constrained param. flag: No
Chroma format: 4:2:0
DCT precision: 8
Pic. structure: Frame
Field topfirst: Yes
DCT type: Field
Quantscale: Nonlinear
Scan type: Alternate
Frame type: Interlaced
Notes:

Leadtek PVR2000 file (Conexant encoder):

Num. of picture read: 107654
Stream type: MPEG-2 MP@ML CBR
Resolution: 720*480
Aspect ratio: 4:3 Generic
Framerate: 29.97
Nom. bitrate: 4000000 Bit/Sec
VBV buffer size: 112
Constrained param. flag: No
Chroma format: 4:2:0
DCT precision: 8
Pic. structure: Frame
Field topfirst: Yes
DCT type: Field
Quantscale: Linear
Scan type: ZigZag
Frame type: Interlaced
Notes:

[pfh]

What would be nice is, if it were possible to change the scan types & Quant. with the same cards and then compare. Seems we get cards that have only one way and that's it, when in fact the chip maybe quite capable of several.

Your question is interesting non-the-less.

Sorry can't answer.