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  1. Basic need: I'd love to hear recommended specs for formatting a video file conversion from MPEG-2 (Tivo) and AVI files to an MP4 file that is similar in relative quality.

    2 scenarios for this need
    :
    • 1. Converting MPG-2 files from my Tivo: I can move Tivo vid files to my PC and convert them to a number of formats. I definitely want MP4 versions so that my kids can watch these animated shows on iPods. I also want the kids to have the option to move the show back to the Tivo for bigger screen watching, but, for the sake of hard drive space, I don't want to have to keep 2 file versions (.tivo and .mp4) of the same show on my PC.
    • 2. Converting downloaded AVI files: Same rationale as #1 above, just a different source for the original files. I have some animated shows in AVI format. I want to convert them to MP4s for iPod purposes, but also want them to look good when we move them over to the Tivo.
    I've experimented with moving both an original AVI file and a converted-to-MP4 file over to the Tivo (Tivo box converts them to the MPG format that it needs on its end, so I'm talking about what kind of file I'm providing it). When I've tried to make the MP4 file match the specs of the AVI (dimensions and bitrate, specifically), the AVI file just looks quite a bit better. Is that always going to be the case? The files I'm talking about are about 180MB for a 22 minute show. Is AVI just always higher quality than MP4 unless I bump the bitrate way, way up? I've tried this and found that it will negate my attempts to save PC space as that gives me something like a 400MB file.

    I use Handbrake and MediaCoder, so I'm good on the techniques to do these conversions. I'm just wondering if I can tweak the MP4s' specs to make them look as good as AVIs.

    Thanks a bunch in advance.
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  2. I'm a MEGA Super Moderator Baldrick's Avatar
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    What video codec? mp4 with h264 video should look similar or even a bit better than avi with divx/xvid using same bitrate.
    What resolution/frame size are you using?

    I like xvid4psp for mp4 h264 conversion. But it should work fine with handbrake also, both are using x264.
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  3. A couple of issues regarding the ipod and conversions. (I don't know anything about tivo)

    1) An ipod compatible settings profile produces very low quality, even though it supports h264. It only supports "baseline" (not main or high), and no CABAC. Max framesize is 640x480, and bitrate <1.5Mbps. So you would likely have to resize as well (unless your framesize fits), but even then you would probably have to add borders to maintain the aspect ratio for a 4:3 screen.

    2) Your source is low quality to begin with. Every time you re-encode using a lossy format it gets worse. A 180MB 22min AVI (assuming) 128kbps mp3 audio) will suggest about ~1000kbps video bitrate which isn't that great...You would be much better off starting with the blu-ray or at least the dvd source.

    If you are constrained to using an ipod profile you can't even raise the bitrate much to compensate and are stuck with using a low quality settings. If you were allowed yourself higher quality settings, you could get similar quality to the AVI file. Therefore I would highly recommend against doing 1 version (don't do the 2 birds, 1 stone thing...)
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  4. Originally Posted by Baldrick
    What video codec? mp4 with h264 video should look similar or even a bit better than avi with divx/xvid using same bitrate.
    What resolution/frame size are you using?


    The original source files are AVI with XVID in the range of 800-1000 kbps and 640x480. I'm using MP4 w/H.264 at 1500 kbps, though I guess upping the bitrate won't help if the source is that low, right?

    I'm just confused why the similarly low-quality AVI looks better.

    I guess a simpler question is "What should my MP4 specs be to match the actual quality of my source AVI?"

    Or is it as simple as the conversion will automatically downgrade the quality no matter what the specs are (like poisondeathray says above)?

    Below is my MediaCoder-generated report on the files:

    SOURCE:
    Hindsight Part 2.avi
    Audio Video Interleave video/avi 179417 KB 22:41
    Video (0)
    XVID
    640x480@23.98fps
    942 Kbps

    Audio (1)
    MP3
    48000Hz 2ch
    128 Kbps


    CONVERTED FORMAT:
    Hindsight Part 2.mp4
    MPEG-4 Audio/Video video/mp4 269106 KB 22:41
    Video (0)
    avc1
    640x480@0.00fps
    1457 Kbps

    Audio (1)
    AAC/AAC+
    48000Hz 2ch
    128 Kbps


    Thanks for the help. Love to hear others chime in on this if there's anything else to add.
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  5. Any re-encoding will downgrade the quality, it's a fact of life. The only exception is if you use a lossless format.

    The quality shouldn't be that much worse @ 1.5x the bitrate using h264 from a 1000kps xvid source, unless you used low quality settings (e.g. ipod profile), in which case you would need to increase the bitrate to compensate

    The specs provided don't say very much, because they don't say what settings you used. I wasn't kidding when I said ipod compatible settings suck. The difference in quality between ipod compatible settings (baseline, no cabac, etc....) and normal settings is large. Here is an example, both at 1000kbps, one using ipod settings, one using "normal" HQ settings

    1000kbps x264 IPOD profile


    1000kbps x264 EQ profile


    If you were restricted to using that low quality profile , you would need to make it roughly 1.5-2x the size to compensate. In other words, you get better quality at the same bitrate (i.e. more efficient) using better settings.


    "What should my MP4 specs be to match the actual quality of my source AVI?"
    .mp4 is just a container. It can "hold" many formats, different types of audio, video, subtitles. What you question should be is what encoder settings should I use?

    If you don't care about the exact bitrate/filesize, and just wanted to maintain a certain quality level, it's faster and probably better in terms of quality to use crf mode (constant quality) encoding. The ending size will vary, but the quality of every frame will be similar. You might use a crf value of 18-22 (smaller value is higher quality/bigger filesize). I don't think handbreak has this encoding mode, but all the other popular GUI's do (e.g. ripbot264, xvid4psp, megui...etc...)
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  6. Always Watching guns1inger's Avatar
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    Your source is, frankly, rubbish. Low resolution, low(ish)bitrate and will gain nothing at all by being converted to H264. Your example above is basically a file that is 50% than the source, for no quality improvement at all. Worse, you are then reconverting a third time (Source -> Xvid -> H263 -> Mpeg2) to get it on your Tivo. By all means convert for the iPod, but if you can feed the Xvid to the Tivo for conversion, you are better off doing that than encoding to mp4 on the way.
    Read my blog here.
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  7. Thanks, guys. Good stuff.

    poisondeathray, I don't use the standard iPod settings as they're obviously intended for a tiny screen. I mainly do DVD-to-MP4 w/Handbrake and will pump up the bitrate. That way, I can have decent quality MP4s on the iPod that can be played out to a TV, which is really nice when the family is traveling and I don't want to drag along our DVD collection.

    guns1inger, good point about the actual number of re-encodes. I don't have the original source, only the acquired XVIDs, so I got them after the first conversion. The quality is good for a PC monitor, but good enough for my kids to enjoy on the big screen (they're not picky).

    The posts have focused on my second scenario (see OP above) which concerned re-encoding XVIDs to H.264 to Tivo. You seem to be familiar with Tivo, so let me reboot my first scenario for you (or anyone else):
    1. Converting MPG-2 files from my Tivo: I can move Tivo vid files to my PC and convert them to a number of formats. I definitely want MP4 versions so that my kids can watch these animated shows on iPods. I also want the kids to have the option to move the show back to the Tivo for bigger screen watching, but, for the sake of hard drive space, I don't want to have to keep 2 file versions (.tivo and .mp4) of the same show on my PC.

    Tivo's Desktop Plus will automatically send its .tivo (mpg-2) files to my PC and convert them for different mobile devices. There is a default H.264 setting that is good for iPods, but not for larger screens. However, there's a tweak floating around (http://tinyurl.com/dyysbu) that allows users to change the settings to increase the re-encode quality. I'm not going to try to kill 2 birds with 1 stone on the XVID convert (because of the repeated degradation), but I'd love to keep the MP4/H.264 version of my Tivo show and dump the .tivo verson.

    So, any recommendations on H.264 re-encode setting for this situation?

    Thanks.
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