Converting HD TV recording to MKV

[son_t]

So UK HD TV is broadcast at 1080i at whatever bit rate is the flavour for this year... I record a whole load of HD stuff and want to convert them to save space on the HDD.

The question is what settings - bitrates, resolution, etc. are good? Are there any general rules, or do I have to experiment and find out what settings are good...?

Is there any reason why I shouldn't drop the resolution to 720p, as I see there's no real lost in detail from 1080i..?

Any advice will be appreciated...

[videobruger]

The question is what settings - bitrates, resolution, etc. are good? Are there any general rules, or do I have to experiment and find out what settings are good...?

I think you should experiment. My personal rule-of-thump: resolution 1280x720, Video: h264 (and that would normally be by x264 - 2-pass) average bitrate: 800 kbps for stuff like TV-shows and 1200-1400 kbps for movies. Audio: AAC at 128 kbps. Container: mp4 or mkv. That suits me.

Is there any reason why I shouldn't drop the resolution to 720p, as I see there's no real lost in detail from 1080i..?

No. On the contarary. You'll get better quality at comparable bitrates, ie filesize.

[MilesAhead]

The only proviso on changing resolution would be processing time. Generally when you size down the conversion takes longer, all other things being equal. I would get a front end for x264 and also check out the docs to get a feel for the command line switches. Maybe use something like AviDemux to cut up a bunch of short clips for testing.

Although going from 1080i to 720p may not slow things down the way going from HD to SD typically does. There's not as much compression going on.

[edDV]

So UK HD TV is broadcast at 1080i at whatever bit rate is the flavour for this year... I record a whole load of HD stuff and want to convert them to save space on the HDD.

The question is what settings - bitrates, resolution, etc. are good? Are there any general rules, or do I have to experiment and find out what settings are good...?

Is there any reason why I shouldn't drop the resolution to 720p, as I see there's no real lost in detail from 1080i..?

Any advice will be appreciated...

How are you playing these MKV files? Media player? Computer?

Is there any reason why I shouldn't drop the resolution to 720p, as I see there's no real lost in detail from 1080i..?

If you don't see a difference, your viewing system is sub-standard.

1080i broadcasts are either true interlace (news, sports, live variety, reality) or progressive sent as interlace (movies and many TV series). Conversion to 720p requires deinterlace in the first case or field weaving in the second before downscale. Native 720p broadcasts are fine as is.

Handbrake is a good choice to do these conversions from a well documented GUI.

DVB broadcasts are already h.264 encoded so go easy on the re-encode bit rate.

[son_t]

Thanks for the replies guys...

So UK HD TV is broadcast at 1080i at whatever bit rate is the flavour for this year... I record a whole load of HD stuff and want to convert them to save space on the HDD.

The question is what settings - bitrates, resolution, etc. are good? Are there any general rules, or do I have to experiment and find out what settings are good...?

Is there any reason why I shouldn't drop the resolution to 720p, as I see there's no real lost in detail from 1080i..?

Any advice will be appreciated...

How are you playing these MKV files? Media player? Computer?

The idea is to play them on the recording device itself (it is a Humax HDR-FOX T2, and can play certain MKV but not all) or on a computer (streamed from a DLNA server).

Is there any reason why I shouldn't drop the resolution to 720p, as I see there's no real lost in detail from 1080i..?

If you don't see a difference, your viewing system is sub-standard.

1080i broadcasts are either true interlace (news, sports, live variety, reality) or progressive sent as interlace (movies and many TV series). Conversion to 720p requires deinterlace in the first case or field weaving in the second before downscale. Native 720p broadcasts are fine as is.

Handbrake is a good choice to do these conversions from a well documented GUI.

DVB broadcasts are already h.264 encoded so go easy on the re-encode bit rate.

Could you go in to detail about this... With my limited knowlege and thinking.... I assume that broadcast is 1080i due to having to send it over the air at a reasonable bitrate and resolution, but once the box has captured the stream, and have been transfered to a PC to be processed, then getting the computer to de-interlaced and 'transcode' to a non-broadcast but better space saving form but still maintaining the PQ is the worthwhile objective..?

The bottom line is: is it worth converting/transcoding 1080i broadcasts to something else, reducing the filesize but keeping the same PQ? If so, what format, what bitrate, what resolution?

[edDV]

Live mode 1080i has 50 motion samples per second sent as 1440x540 fields. This gives smooth motion for sports or live variety. The HDTV will expand interpolate the 1440x540 fields to 1920x1080 for display. These will be displayed as 50p with full motion detail.

Movie mode 1080i produces 25 motion samples per second sent as 1440x540 fields but with both fields from the same motion sample. These two fields can be woven into 1440x1080 progressive frames at 25 fps. The HDTV expands each frame to 1920x1080 and repeats frames to 50 fps for display.

Both modes are sent h.264/AC3 at about 17 Mbps (e.g. BBC-HD). These can be distributed as is through DLNA for a high speed network, but for wireless and slower networks, the DLNA server will attempt on-the-fly recompression to lower bit rate. Since it is doing this real time, the picture quality results can be poor.

If you want to optimize for DLNA playback or for web or handsets, you can re-encode to much lower bit rates but there will be quality loss. Extreme compression will require deinterlace of 50i "live mode" to 25p (half the motion samples) at 1440x1080 same as movie mode. Then for both modes you can reduce resolution to for example 1280x720 and lower bit rates.

[son_t]

[QUOTE=son_t;2138986]Thanks for the replies guys...

So UK HD TV is broadcast at 1080i at whatever bit rate is the flavour for this year... I record a whole load of HD stuff and want to convert them to save space on the HDD.

The question is what settings - bitrates, resolution, etc. are good? Are there any general rules, or do I have to experiment and find out what settings are good...?

Is there any reason why I shouldn't drop the resolution to 720p, as I see there's no real lost in detail from 1080i..?

Any advice will be appreciated...

How are you playing these MKV files? Media player? Computer?

The idea is to play them on the recording device itself (it is a Humax HDR-FOX T2, and can play certain MKV but not all) or on a computer (streamed from a DLNA server).

Is there any reason why I shouldn't drop the resolution to 720p, as I see there's no real lost in detail from 1080i..?

If you don't see a difference, your viewing system is sub-standard.

1080i broadcasts are either true interlace (news, sports, live variety, reality) or progressive sent as interlace (movies and many TV series). Conversion to 720p requires deinterlace in the first case or field weaving in the second before downscale. Native 720p broadcasts are fine as is.

Is this because I am viewing the output on a 37" HD Ready (720p, not Full HD) TV? Would I notice the difference if I was to view the converted video on a 42"+ 1080p TV?

[edDV]

Is there any reason why I shouldn't drop the resolution to 720p, as I see there's no real lost in detail from 1080i..?

If you don't see a difference, your viewing system is sub-standard.

1080i broadcasts are either true interlace (news, sports, live variety, reality) or progressive sent as interlace (movies and many TV series). Conversion to 720p requires deinterlace in the first case or field weaving in the second before downscale. Native 720p broadcasts are fine as is.

Is this because I am viewing the output on a 37" HD Ready (720p, not Full HD) TV? Would I notice the difference if I was to view the converted video on a 42"+ 1080p TV?[/QUOTE]

Yes on a 1080p TV. The difference will be greater the closer you sit to the TV and/or the larger the screen.