I'm gonna give changing the resolution/bitrate a try, and see what happens.

Why 720x480, though?

I'm watching these on a regular, plain ol' television. Nothing fancy. Also, since I am doing this just to save space, are there some other alternatives I should explore?

Thanks for your help!

_________________
- Anthony
- P4/1.8GHz, 768MB RAM, PVR-150, GeForce FX 5200

This is covered in the R5F27 Hints along with a link to the original discussions in the IVTV mailing list.

720x480 is the standard resolution used for all analogue OTA & cable transmissions in the US (NTSC). While 480x480 is also supported by many devices, over the years various devices and software packages have exhibited on-again, off-again problems at 480x480. In general, I like to keep my SD recordings at 720x480 to avoid these types of problems.


Yes there are -- consider the following list of "factoids" and suggestions:

• The size of your recording is not directly effected by the resolution you choose. The size is determined by the bitrate.
  
• Factiod: Having said this, higher resolutions require a higher bitrate to look better.
  
• factiod: You are currently recording at 6,000 kbps at 480x480. This is a very high bitrate which will yield file sizes in the range of 3.5GB/hour.
  
• Suggestion#1: My experience is that I achieve acceptable results at 720x480, 3,300 kbps displayed on my 50" rear-projection DLP. This will yield file sizes in the range of 1.8GB/hour. I suggest giving this a try.
  
• Suggestion#2: My previous TV was a 32" trinitron. At that time I used 352x480 at 2,200 kbps. This yielded file sizes in the range of 1.2GB/hour. 352x480 is a supported resolution in the NTSC standard. At that time (2 years ago) the only problem I ran into was with creating DVDs. The version of mythburn (now called mytharchive) that existed at that time did not work properly with 352x480 resolution recordings. I don't know if this is still an issue. In my case, I didn't consider this a show stopper.

The easiest way to changes your bitrate and resolution is in "recording profiles"->mpeg2 encoders->default. I would start with setting both the bitrate and max bitrate to the same value. This is known as CBR (Constand Bit Rate) encoding.

If you are so inclined, you can experiment with setting the max bitrate up to 50% higher than the overall bitrate. This is call VBR (Variable Bit Rate) encoding. As an example if you set bitrate to 3300 and maxbitrate to 4400, the mpeg2 encoder will attempt to allocate more of the bandwidth (up to 4400kbps) to high-action scenes. It will reduce the bitrate allocated to low action scenes to less than 3300kbps so as to maintain an overall average bitrate of 3300 kbps, thus yielding file sizes that are the same as CBR 3300kbps. My experience from a few years ago was that VBR encoding with the PVR-150/PVR-250 hardware did not work well, but I've read notes from other folks who felt otherwise.

It is worth noting that recording at a higher bitrate to mpeg2 and then transcoding to mpeg4 (divx) should, in theory, yield a better result in a more compact filesize then my above suggestions. In reality:

• The quality of the transcoded video is heavily dependent on getting the transcode procedure setup properly. The codec's have many configuration parameters, and getting to the best outcome can be difficult. I haven't tried enough samples on R5F27 to comment on the quality of the myth transcode result under all circumstances, although the results I saw with my sample yesterday looked promising. In past releases I have found that sometimes the transcoded videos worked out well and sometimes they didn't, so I didn't use transcoding.
• Transcoding is CPU intensive. On some systems transcoding while recording can result in glitches in the new recording.

Marc

I take a somewhat different approach from Marc. My recording profiles are set at 720x480 (both for proper operation with the ivtv drivers and DVD compatibility) with a variable bitrate of 6000-8000kbps. I then do lossless transcoding to remove non-content.

This typically ends up with a "half hour" program (typically 22-24 minutes of real content) taking 0.9 to 1.1Gb of disk space, and a "one hour" program taking roughly 1.9-2.2Gb (depending on how much cruft there was). Monsters Inc. was a 2 hour recording with only 1:32 worth of content and it came in at 4.2Gb. When you come right down to it, disk space is even cheaper than blank DVDs.

TJC, your approach makes a lot of sense. Do you use commflagging to identify which content can be eliminated? If so, does this approach ever result in the loss of material you wanted to keep? ie, Part of the program being mis-identified as a commercial...

Marc

I use commflagging to get a starting point, but I always verify and hand edit the cut points before transcoding (or generally even before watching something I intend to delete immediately). With a little bit of practice and a wireless keyboard this goes very quickly. The correctness of automatic commflagging results varies wildly based on the channel and content.

tjc and marc --

Thanks for all your advice and help! tjc, I read everything on the hints and couldn't find a link to the ivtv mailing list -- I'll certainly keep looking though (I was at work and may have overlooked it).

Changing the bitrate and resolution (I've been doing a bit of experimenting) didn't seem to do much for the audio problem on the transcoded files.

Could you maybe take a look at what I have?

Settings -> TV Settings -> Recording Profiles -> Transcoders

(For some reason, mine are all identical ...)

For High Quality:

Profile
Profile Name: High Quality
Custom Filters: (blank)
Lossless Transcoding: (not checked)
Resize Video while transcoding: (checked)

Image Size
Width: 720
Height: 480

Video Compression
Codec: MPEG-4
Bitrate: 1300
Maximum Quality: 2
Minimum Quality: 15
Max quality difference between frames: 3
Scale bitrate for frame size: (unchecked)
Enable high-quality encoding: (unchecked)
Enable 4MV encoding: (unchecked)
Enable interlaced DCT encoding: (unchecked)
Enable interlaced motion: (unchecked)

Audio Quality
Codec: MP3
Sampling Rate: 32000
MP3 Quality: 7
Volume: 90


Does this look normal? Is there any other information I could share? Would adjusting the sampling rate of the audio maybe have some positive effect? It says that btaudio will only accept 32000, so I might not have a choice.

I think, since I only plan to watch something and then delete it (except for very few shows) I'll disable transcoding for now. I have plenty of space for the shows that I'd like to watch (and then thereafter delete) so it's not a big deal.

Thanks again, y'all!

_________________
- Anthony
- P4/1.8GHz, 768MB RAM, PVR-150, GeForce FX 5200

It's indirect via both their troubleshooting page http://ivtvdriver.org/index.php/Troubleshooting and this thread http://mysettopbox.tv/phpBB2/viewtopic.php?t=13097
http://www.gossamer-threads.com/lists/ivtv/devel/33031#33031

Two comments:

1. In your post you talk about having changed the transcode profile to 720x480. In my post I was talking about changing the recording profile to 720x480. The point is to make the initial recording in 720x480.

2. The transcode profile has a setting which essentially says "leave the resolution of the output file the same as the resolution of the input file". If your original recording is 720x480, your transcoded output will also be 720x480.

3. Make sure you are modifying the right profile. On my setup, everything uses the "default" profile, not the "high quality" profile.

Marc

Oops, didn't mention that I did that as well when you first recommended it.



Did that last night -- not sure why I was using all different profiles when they had the same settings, anyway.

Thanks!

_________________
- Anthony
- P4/1.8GHz, 768MB RAM, PVR-150, GeForce FX 5200

I dropped in an AGP GeForce FX5200 to replace the PCI one I had in there.

Stuttering solved. I'll try transcoding something and playing it back, just to see if it works with that, as well.

EDIT: Transcoded videos play well, too!

_________________
- Anthony
- P4/1.8GHz, 768MB RAM, PVR-150, GeForce FX 5200