[mythtv-users] Building a library.....chews up space!!

[Andre]

On 28 Mar 2011, at 18:37, Raymond Wagner wrote:

> On 3/28/2011 09:39, Another Sillyname wrote:
>> I take broadcast HD source material and transcode it using my own
>> scripts to about 25-35% of it's original size, if you include the
>> advert cuts the savings are huge.
> 
> H264 was only ever designed to handle about double the compression 
> efficiency of MPEG2, and if using comparable quality compressors from 
> both, that estimate tends to hold true.

That figure is only meaningful when encoding mpeg2 and h264 from the same (usually uncompressed) source material!

Encoding h264 from an already maximally compressed mpeg2 (US HD) source isn't going to give you equivalent quality going to the same bitrate/filesize as the original recording! Thankfully most broadcast is live encoded and has bit stuffing to make up bandwidth also multi audio tracks, subtitles and other data that can usually be discarded.

I find that for mpeg2 HD broadcasts I can get equivalency at about 80% of the original recording size and acceptable to almost all at 50% size. For UK H264 HD recordings the size stays about the same, sometimes a little more. 

Most people seem happy at 20% to 30% size but when building a library you need to think about the future a little, what looks ok on your current TV may look like 80's VHS two TV's along, especially when better h264/mpeg2 decoders come along and you have thrown away 80% of the information because on your current TV/ decoder it didn't look any different.

When DVD players came along they made VCDs look a great deal better than VCD players did! If you have re-encoded those VCDs to equivalent mpeg2 quality the benefit of better playback decoding would have been lost. There is a great deal in the h264 spec that isn't fully utilised yet, for playback as well as for encoding, it's highly likely future decoders will be able to render better quality images from the same data, there is already a great deal of variation. 

No-one has build a videophile h264 decoder yet...

What is worth a go is pure remuxing, no image quality is lost, just those padding bytes, teletext, eit, subtitles and a lot of timing packets that are needed for live broadcast but not for file playback (if you stream they are re-created anyway), you can save 30% by remuxing to a simpler ts file or a little more if you go to mkv or mp4, no nuance of the video is lost as you never alter the encoded video. 

If you in the US and your broadcaster transmits movies & filmed drama with 3:2 pulldown encoding, many do because it saves bandwidth, then you can remove these and be left with a 24p video, you'd have to remove the ads first as they wouldn't be 3:2 pulldown encoded but you would want to do that anyway right?

My 2p/c/€c

Andre