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| Unofficial VirtualDub Support Forums > Newbie Questions > Capture File Sizes |
| Posted by: chrisstephens Aug 29 2013, 03:31 AM |
| Today I started on a project to capture video from VHS machine using a Pinnacle Dazzler DVC100 (I would use Pinnacle Studio but lost the CD). Now, I get the raw video quality is crap (25 year old tapes), but, I am trying to understand why the capture file size is still so much larger compared to other video files. For instance, I looked at two movies I (cough) obtained. This is the info in the codec stats from VLC plus the estimated file size/minute video1.avi - 787,256 KB - 1:48:38 -> ~108.5 Min -> ~7,255 Kb/Min -> ~7 MB/Min Stream 0 Type:Video Codec: MPEG-4 Video (XVid) Resolution 720 x 448 Frame rate: 23.970 Stream 1 Type: Audio Codec MPEG Audio Layer 1/2/3 (mpga) Channels: Stereo Sample Rate 48000 Hz Bitrate 128 kb/s video2.mp4 - 1,124,205 KB - 1:26:00 -> ~86 Min -> ~13,072 Kb/Min -> ~12.76 MB/Min Stream 0 Type:Video Codec: H264 MPEG-4 AVC (part 10) (avc1) Resolution 720 x 494 Frame rate: 23.976023 Stream 1 Type: Audio Codec MPEG AAC Audio (mp4a) Channels: Stereo Sample Rate 48000 Hz Now, both of these videos look pretty good played in VLC. The video quality is sharp with little if any pixelating or distortion. But when I import using VLC, the file sizes (even with compression) are considerably larger. For instance, I copied about 16 minutes of VHS tape (which looked decent enough without any compression artifacts), and the file size was 369,852 MB. So about 23 MB/Minute of video. I used the DivX codec (downloaded and installed today, so the most recent), and configured it with the following settings: Video->Capture Pin -> 29.976 frame rate, 640x480 output size Video->Compression-> DivX Configure -> Home Theater Profile, 1-pass, 3000 kbps Audio->Compression-> LAME mp3-> 48000hz, 160 CBR Stereo So, while my capture is about 23 MB/Min, even a high quality file like video2 was still only 12 MB/Min. Of course, the VHS having a 29 vs 23 frame rate would explain a 25% increase in file size, but why does it still seem so large? If I reduce the bit rate to something like 1000, the file size is lower but there is noticeable loss on playback. The only thing I could figure is that the proper way to do this would be to capture lossless (which would be like hundred gigs for a an hour or so) and then run it through a program that might be able to provide a variable bitrate compression or better compression from raw-file->compressed-file versus doing it on the fly with a direct input from a video source (or would this even matter?) |
| Posted by: dloneranger Aug 29 2013, 05:27 AM |
| Most codecs (including divx) have options for speed/quality, where the longer it takes to compress, the better quality (or smaller size) it makes - divx on 'fastest' can produce truly horrible results, but on highest is very nice Of course, as divx is a commercial codec, you have to pay for a key to use it's best quality modes I'd suggest XVid instead of Divx as it's free, and has comparable quality/size X264vfw will give smaller files for the same video, but needs a faster cpu to process at the same speed as XVid Instead of capturing uncompressed, you could also use a lossless codec as they're very quick and while their files are larger than DivX, are a lot smaller than uncompressed (I'd suggest Lagarith http://lags.leetcode.net/codec.html) If your pc can keep up then capturing and compressing to X264 or XVid would be fine, but means you can't try out things You could of course capture 5 minutes or so uncompressed (or lossless codec - lagarith, huffy, utvideo), and then try different settings of your codec to find out what works best for you Re bitrates, Unless you're hell bent on hitting an exact file size, don't bother using a bitrate setting (1pass bitrate settings are even worse for quality as you'll be using all that bitrate even on totally static scenes) Most codecs have another way of encoding, using a constant quality setting instead, where the quality of the video will stay the same, but the bitrate will adjust to fit what's needed You'll usually get better results with less trouble using that XVid on a setting of 4 or 5 will give good results, and x264vfw settings can be seen here http://forums.virtualdub.org/index.php?act=ST&f=4&t=21157&hl=x264vfw In XVid, the mode you'd use is '1 pass -quality', where the smaller the number for quality is, the better quality you get The settings are explained in this pdf http://nic.dnsalias.com/XviD_Options_Explained.pdf Note: In constant quality modes, the extra quality settings of the codec will change the final file size - the longer it takes to compress, the smaller the file will be If you do actually need a precise file size, then 2 pass encoding is the best way to get a decent size/quality |