File Formats

Good: MPEG 2 (DVD)

MPEG 2 comes in two flavors. The type of MPEG 2 file written on a DVD disk is called Program Stream and stores data in 2048 byte chunks (which is the native size of one block of data stored on a DVD). The type of MPEG 2 broadcast by TV stations or transmitted on a cable TV system is called Transport Stream (TS) and formats data in 188 byte chunks. These smaller units are needed to minimize loss and simplify recovery when there is interference with a signal broadcast and received by an antenna, but they are inefficient when data is stored on a disk. So while the TS format may be initially used when a broadcast or cable program is first recorded, after you edit it to remove commercials you will probably convert it to Program Stream for long term storage.

When Microsoft began to offer its Media Center option, it required a hardware encoding chip on any TV tuner that could take over all the work of compressing a digitized version of the standard definition analog TV program. This is probably a good idea in any event, because when the encoding is done on the card there is so little demand for CPU that a single computer can easily record 4, 6, or more TV programs all at the same time. Recording standard definition analog programs as an MPEG 2 stream was also attractive because there are several programs that can convert an MPEG 2 recorded program directly into the disk file structure used for video DVD disks. The recorded program can then be burned directly onto a DVD-R for long term storage.

Both the FCC digital TV standard and the DVD movie file format combine both picture and sound. In fact, they support several alternate sound tracks typically in different languages. So MPEG 2 provides two comprehensive file format standards.

Better: MPEG 4,  Divx and Windows Media (WMV)

The simple versions of MPEG 4 represent the highest compression or best quality that can be recorded in real time on a current computer. Unfortunately, while lots of devices have hardware MPEG 2 encoding on the board, and while simple MPEG-4 encoding chips have been available for several years, only one vendor produced a PC product that provided hardware MPEG 4 encoding.

Therefore, Divx and Windows Media tends to be an option when the tuner card does not do any compression and the data is compressed instead using the CPU. That is fine if you are only recording one program at a time. Given the current mix of hardware, you will have trouble trying to do MPEG 4 compression using the CPU for two or more programs at the same time.

MPEG 4 is simply a video compression standard. There is no generally accepted file format. Microsoft has the WMV format, Divx has its format, or you can create AVI files. Every software package has its own way of adding the audio part, and players do not always accept every version.

Best: MPEG 4 Advanced, H.264

The best video encoding standard is the advanced version of MPEG 4 described in "Part 10" of the standard. The problem is that current computer hardware cannot compress video using this standard in real time. Generally you have to capture the program using one of the other standards, and then overnight you can recompress it to advanced MPEG 4 at a slower pace. Typically you will need to run your dual core CPU at 100% for six hours to recompress one hour of HD video.

However, computer chips always get faster, and the particular operations required to compress video are one of the areas to which chip vendors pay particular attention. Some of the processing can get turned over to the unused capability of the video adapter Graphics Processing Unit. This may reduce the amount of time required for overnight processing, but at this time it would be speculative to predict that future systems will be able to do real time advanced MPEG 4 encoding of a program as it is received by the TV tuner.

Blu-Ray and HD DVD disks have standard formats for advanced MPEG 4, but they have not had the influence over file formats that the DVD had. It is too soon to determine if a file standard will emerge.