Another Unbox thread... uneven video quality?

Discussion in 'TiVo Coffee House - TiVo Discussion' started by MickeS, Aug 6, 2007.

  1. Aug 6, 2007 #1 of 34
    MickeS

    MickeS Active Member

    25,977
    24
    Dec 26, 2002

    Advertisements

    Before this weekend I had seen 4 Unbox movies and 1 Unbox TV show: Epic Movie, Night at the Museum, The Bourne Supremacy The Bourne Identity and an episode of South Park.

    I have been happy enough with the quality of them - seemed to be like about "Best" TiVo recording.

    But this weekend I watched "The pursuit of Happyness" and "Ghost Rider" and I noticed something that I had not seen before. There was an annoying "lag" in some scenes were objects moved quickly. It looked kind of like the Windows mouse pointer does when you turn on "Display pointer trails", although not as severe.

    The odd thing is that it wasn't in all scenes, and it mainly seemed to happen with larger objects. For example, a crowd scene in "Ghost Rider" where the spectators at a Johnny Blaze jump are all waving those big foam hands, and clapping and generally moving didn't have any effect like it at all, even though there was constant motion all across the screen. But a simple dialog scene between Cage and Mendes had it every time they moved across the screen. I took some screenshots, but can't find a USB cable to connect the camera. :)

    Has anyone else seen this? Is it possible that I have never noticed this before (which seems odd), or is the quality of the videos so uneven?

    This really looked awful... whether I just happened to not notice it before or not, if this was my first Unbox rental, there probably would not have been anymore.
     
  2. Aug 6, 2007 #2 of 34
    Dan203

    Dan203 Super Moderator Staff Member TCF Club

    52,786
    6,763
    Apr 17, 2000
    Nevada
    I've seen it on a few Unbox videos as well. I think the worst one I saw was Casino Royal, which had several scenes which were just painful to watch.

    Glad to hear the "Bourne" movies are OK though. I was going to download them to watch again before seeing the new one, but I was a little worried about the quality after having watched Casino Royal. Sounds like they're OK though, so I think I'm going to give them a shot.

    Dan
     
  3. Aug 6, 2007 #3 of 34
    flip123

    flip123 Member

    62
    1
    Feb 10, 2003
    I agree. I have rented 13 Unbox movies. 11 of them have been just fine. "Casino Royal" and "The Pursuit of Happyness" were almost unwatchable at times.

    Phil
     
  4. Aug 7, 2007 #4 of 34
    MickeS

    MickeS Active Member

    25,977
    24
    Dec 26, 2002
    I uploaded the pictures I took, so I might as well post them. :)

    [​IMG]
    [​IMG]

    And this one, where the crowd moved, but there was no "lag" effect:
    [​IMG]

    So do you guys think these are encoding mistakes, or done intentionally for whatever reason?
     
  5. Aug 7, 2007 #5 of 34
    Dan203

    Dan203 Super Moderator Staff Member TCF Club

    52,786
    6,763
    Apr 17, 2000
    Nevada

    Advertisements

    One possible explanation for these quality problems could be framerate conversion. TiVos only support video with a frame rate of 29.97fps. Some movies are actually filmed at 24fps. That means that Amazon has to use some sort of framerate conversion to make them compatible with TiVo. There are various methods for doing framerate conversion, and some work better then others. These sort of motion artifacts are actually characteristic of some of the poorer techniques.

    If it is a framerate conversion problem, then it would explain why it only effects some movies as only some use the 24fps "film mode".

    Dan
     
  6. Aug 7, 2007 #6 of 34
    gonzotek

    gonzotek tivo_xml developer

    2,538
    59
    Sep 24, 2004
    Outside...
    This is exactly what I've thought the problem was since Unbox came out and the first movie I tried exhibited the symptom. I've converted a lot of video for a lot of different kinds of devices by now, and I've had it happen plenty of times. And like you said, there are techniques that can produce much better results. If they want it to succeed, TiVo and/or Amazon really need to investigate and re-encode the problem downloads. I hate the feeling of gambling I have every time I want to use Unbox, betting that I won't get a poorly encoded file. When they play back correctly, I'm happy with the service, but when my wife and I sat down to watch Ghost Rider, she complained that it actually hurt to watch.
     
  7. Aug 7, 2007 #7 of 34
    MickeS

    MickeS Active Member

    25,977
    24
    Dec 26, 2002
    I bet you are right! That is a BIG oversight for an operation like this. :thumbsdown:
     
  8. Aug 8, 2007 #8 of 34
    refried

    refried Member

    147
    1
    Dec 21, 2005
    Brunswick, ME
    I've been mostly happy with the video quality of Unbox downloads thus far. I was amazed at the great quality of "The Devil Wears Prada." Since then, I've watched several movies. "Stranger than Fiction" and "The Good Shepherd" were both good this weekend. The only video I didn't like the quality of was the free "Jericho" episode. It had a lot of horizontal artifacts. I ended up deleting it since my recently recorded off-the-air version looked a lot better.
     
  9. Aug 8, 2007 #9 of 34
    Stu_Bee

    Stu_Bee New Member

    887
    0
    Jan 14, 2002
    Silicon...
    'Letters from Iwo Jima' had somewhat jittery subtitles on my 42".
     
  10. Atomike

    Atomike New Member

    292
    0
    Jun 12, 2005
    This is not the problem. ALL movies are shot in 24 frames per second - it's the rate film is recorded as an industry standard. ALL films are then converted to 29.97 fps - it's a process called 3:2 pulldown, and it is done all the time every day. If this was the problem, then all GhostRider DVDs would also exhibit this problem, since all DVDs are also converted to 29.97 fps (for north American NTSC anyway).
    The more likely explanation for this problem is simply that the Tivo hardware can't keep up with the motion-intense bitrate of these scenes, since they are almost certainly encoded at a variable bit-rate. As the complexity of the scene increases, so does the bit rate. You will sometime see these problems in low-end DVD players for the same reason, and is likely the reason you see it in other cheap hardware.
     
  11. MickeS

    MickeS Active Member

    25,977
    24
    Dec 26, 2002
    You're forgetting that it's possible that Amazon receives some source material in 24fps and some in 29.97 fps, but that for some reason they have used the same way of converting them.

    There was nothing particularly motion-intense about the above scenes that I took screenshots of. I have played MPEG2 material on my Series 2 that was taken directly from full-bitrate DVDs and never had a problem even with the most motion intense scenes. I seriously doubt that these lower-bitrate Unbox files would be any problem for a Series 3.
     
  12. Atomike

    Atomike New Member

    292
    0
    Jun 12, 2005
    Hmmm. Not to be sarcastic, but do you think that Tivo (or Amazon) is sent rolls of film like the ones projected in movie theatres? No - I'd bet a donut that Tivo is SENT the film in a digital format, likely the same mpeg2 files that are on the DVD you buy at the store. Does it make any sense to anyone that Studios would send raw film? If it's not raw film, it's not 24 fps - It's 29.97 NTSC. Even if Tivo does the encoding, it would all be done from a 29.97 NTSC format sent from the studio.

    Also, although the images may not look complex to you, an encoder can find difficulty where the human eye cannot - many pixels may look similar, but are not. A completely white screen may in fact have each pixel as a slightly different shade, causing the bitrate to be be surprisingly large.
     
  13. pdhenry

    pdhenry Ruthless

    30,444
    5,914
    Feb 27, 2005
    PA
    This isn't a new Unbox problem. All NTSC video is 29.97 fps - any film to video conversion has to deal with the 24-->29.97 conversion. Obviously there are known ways to do it right or we'd have been complaining about DVDs years ago.
     
  14. MickeS

    MickeS Active Member

    25,977
    24
    Dec 26, 2002
    I think the fact that you think film-based content on DVDs has to be stored as 29.97 fps NTSC says enough about your expertise in this area. I'm glad you're not sarcastic though! :D
     
  15. lrhorer

    lrhorer Active Member

    6,933
    10
    Aug 31, 2003
    San...
    That's not quite true. It is one industry standard, but not the only one. It is the most common. Imax films, for example, are shot at 60fps. Not only that, but many films today are shot in part on video. Also - I know this is a nitpick - it's the playback which is 24fps, or whatever. The film may be shot at 1 frame per second or even per minute, hour, or day for time-lapse photography and 100 fps or even faster for slow motion photography.

    True.

    I seriously doubt that. After all, these are 480i SD content, and the TiVo can easily handle 1080i HD content whose compressed bitrate is over 5 times the bit rate of an SD stream. Note, however, the compressed bitrate does not vary only with scene complexity, but also with the level of compression. A highly compressed stream is harder to handle than a less compressed stream of the same content. On the other hand, the main burden is on the processor doing the compression, not the decoder.

    Yes, but the bit rate of even the most complex SD content doesn't match the bit rate of the average 1080i offering. Not only that, but the scenes they showed in the sample screenshots didn't look very complex. Of course, it's hard to say just from a still photograph, but the really difficult and complex scenes are things like drifting smoke, waving filelds of grain, or a swirling mob of people seen from above form a moderate distance. If every single pixel of the scene changes in value from one frame to the next, then it takes a huge bandwidth to comunicate the changes in the screen. If large areas have only moderate or no change from frame to frame, then communicating the changes takes much less bandwidth.

    If someone has one of these Unbox videos on their PC, they could measure the bitrate in these areas to see just how high it is. I'd also be interested to know if they see the same artifacts on their PCs.

    This begs the question, however. Why is there a problem with the Unbox videos and not the ones from CATV? I only have 1 Unbox video at this time. It's Hook with Robin Williams, Dustin Hoffman, and Julia Roberts. I'm not pleased with its quality, but only because it is SD, not HD. Nonetheless, it's average bitrate is 3.07Mbps. This falls pretty much in line with other SD recordings off CATV sources such as Finian's Rainbow at 2.70Mbps and Nova at 3.30Mbps. Compare that with HD offerings like Cellular at 16.0Mbps, Arthur at 13.0Mbps, and Planet Earth at a whopping 16.5Mbps average bit rate.
     
  16. Dan203

    Dan203 Super Moderator Staff Member TCF Club

    52,786
    6,763
    Apr 17, 2000
    Nevada
    While it may be true that most movies are shot at 24fps, not ALL are converted to 29.97fps by the studio. For DVDs 24fps "film mode" is a legal framerate, so there are movies out there that are simply encoded to MPEG2 in their native 24fps. The reason most studios do the conversion on their end is because when a DVD is in 24fps "film mode" it has to depend on the hardware in the DVD player to do the 3:2 pull down. And since, as you pointed out below, there are some really cheap and crappy DVD players out there most studios do the conversion on their end to prevent quality problems.

    I have no idea where, or in whatformat, Amazon is getting their content. I assumed that they were simply ripping it from DVDs or using the same MPEG2 data stored on DVDs as their source. However it could be anything from uncompressed original digital conversions to already compressed MPEG4. But in any case it's still possible that the source is 24fps and is having to be converted to 29.97fps for TiVo. (PCs using the Unbox software can play 24fps content just fine, so the TiVo version would be the only one that needed converting)

    In any case it was just a theory. Only Amazon, and possibly TiVo, knows what the real problem is.

    As pointed out above the quality issues exist even on the S3 units, which have more then enough power to decode HD at 10 times the bitrate of Unbox movies. So seriously doubt this is a hardware issue within the TiVo itself.

    Dan
     
  17. lrhorer

    lrhorer Active Member

    6,933
    10
    Aug 31, 2003
    San...
    TiVo, meaning TiVo, Inc. isn't sent anything. This is an Amazon.com service hosted and maintained by Amazon.com. A TiVo is not required to utilize the service, nor does one have to own a TiVo or have any contract with or obligation to TiVo, Inc. to make use of the Unbox service. I'me sure TiVo gets a little bit of money from Amazon every time someone downloads an Unbox video to their TiVo, and there might be something with the TiVo hardware which is causing a problem with the Unbox videos not seen when using a PC, but TiVo, Inc. doesn't touch the video content.

    Well, half true. The first copy of the frame - probably an I-frame - would take a large amount of data. Subsequent frames would not take large amounts of data unless every pixel in the screen were changing. This would be noticed by the human eye. What's more, the reverse is not true at all. If it looks"busy" to the human eye, then it will be "busy" to the video processor. For that matter, a sudden change from solid black to solid white takes a large momentary burst of data. 'not as muchas from black to raster, but a heap nonetheless. So far, no one is reporting problems with visually busy scenes, just these apparently fluid scene transitions.
     
  18. Atomike

    Atomike New Member

    292
    0
    Jun 12, 2005
    Dude, read a Wiki or something before you post again. While it's possible that a DVD is 24 fps, you don't own one, and have never watched one. It almost never happens. Name a title you own thats encoded at 24 fps. I'll wait for your response.
     
  19. snathanb

    snathanb New Member

    462
    0
    Sep 13, 2006
    I think, perhaps, you need to do some reading. You seem to be confusing the encoding rate with the decoding rate.

    Most film-based DVDs are encoded at 24 FPS and then decoded by the player for playback at 29.97 fps. The encoding includes telecine flags to indicate it needs 3:2 pulldown processing.

    Quoting from another post on another site
    "
    Take any modern commerical DVD and open the VOBs in DGIndex. If you decode with "Honor Pulldown Flags" enabled, the decoded framerate will actually be 29.97i. If you decode with "Forced Film" enabled, DGIndex will simply assume framerate to be 23.976 fps and ignore all the repeat flags. If the DVD was encoded with a good encoder (these days most commercial DVDs are), the entire film will come out as pure 23.976p.
    "
     
  20. MickeS

    MickeS Active Member

    25,977
    24
    Dec 26, 2002
    Keep digging! ;)

    I really have no idea why some Unbox videos have this defect and other's do not, but it doesn't seem unlikely to me that the original frame rate has something to do with it.

    I'm trying to find somewhere to contact Amazon about it, but no real luck... I HATE their Unbox site.
     

Share This Page

spam firewall

Advertisements