Yo
13th August 2004, 08:40
I am having a strange audio occurence this evening, using vdubmod 1.5.10.1, in Windows XP Pro SP1.
I encoded a small clip (6:19 minutes) of an MPEG-2 video, to AVI, in order to experiment with different video properties. As the audio wasn't a concern, except to see if it was still in sync, I just had the audio stream set to "Direct Stream Copy". From what I understand, that means no changes in the audio--input=output.
I was surprised that the file size of the created DIVX AVI was larger than the original MPEG-2, as the video should have been compressed a lot. In looking further at the properties of the created AVI, I saw that the size of the video was indeed much smaller than the original. However, the file size of the audio was MUCH larger than the original, in fact much larger than the video! The audio had been totally uncompressed.
I'll give more detailed properties, as shown in "File Information" in the File menu in VDubMod:
Original MPEG-2 File:
Video--average bit rate- 1032 kbps
Audio--48khz stereo, 224kbps Level 2
total audio size 10,390K
(The total video size wasn't given. The file size of the combined MPEG-2 file was 59,779 KB.)
Stats of the AVI file after video compression, but with audio set to "direct stream copy".
Total file size: 74,712 KB
Video--
Data rate: 63 kbps
Audio--
Data Rate: 1536 kbps (while the original was 224 kbps!)
again sampling 48khz, stereo 16 bit
here is the clincher-under "Audio Tag":
"Tag: 0x0001, Not decodable
Microsoft PCM Format
PCM (uncompressed)"
So, apparently the audio coming out of "Direct Stream Copy" was not the same coming out as going on, but had been totally uncompressed. Does anyone know what that tag means?
Thinking that perhaps there was something about the original audio that was non-standard, that caused a problem for VDubMod, I decided to demux and transcode it. Using TMpgenc, I demuxed the mpeg-2 clip mentioned above. The resulting .mpv file was 47,877 KB, and the .mpa file was 10,390 KB.
I then transcoded the .mpa file with BeSweet (using the BeSweet GUI), to one of the presets, to create .mp3 audio at 128 kbps.
The resulting MP3 file was 5,935 KB in size. I then muxed it with the .mpv file using TMPGENC. The resulting .MPG file was 54,497 KB in size, a little smaller than the original (before transcoding the audio) 59,779 KB.
I loaded the new version of the MPEG-2 clip (with the BeSweet transcoded MP3 audio) into VdubMod. Properties shown-video same as original clip--1032 kbps. Audio 48khz joint stereo, 128 kbps layer III. And of course--file size-- 5935k.
I once again set it to save to AVI--exact same video settings as before, and again audio--"Direct Stream COpy".
Once more--resulting AVI with video much more compressed ends up much larger in file size than the original MPEG-2 file, 74,598 KB.
Its properties:
video data rate, same as other AVI (video compression was the same),63kbps.
Audio-also exactly the same as the other AVI, data rate 1536 kbps, `same tag, "not decodable", etc.
------------------
What is causing this problem? What is causing the "direct stream copied" audio to end up much larger than the original? What does that tag mean? Why "not decodable"?
I would appreciate any input anyone can give me into this problem.
I encoded a small clip (6:19 minutes) of an MPEG-2 video, to AVI, in order to experiment with different video properties. As the audio wasn't a concern, except to see if it was still in sync, I just had the audio stream set to "Direct Stream Copy". From what I understand, that means no changes in the audio--input=output.
I was surprised that the file size of the created DIVX AVI was larger than the original MPEG-2, as the video should have been compressed a lot. In looking further at the properties of the created AVI, I saw that the size of the video was indeed much smaller than the original. However, the file size of the audio was MUCH larger than the original, in fact much larger than the video! The audio had been totally uncompressed.
I'll give more detailed properties, as shown in "File Information" in the File menu in VDubMod:
Original MPEG-2 File:
Video--average bit rate- 1032 kbps
Audio--48khz stereo, 224kbps Level 2
total audio size 10,390K
(The total video size wasn't given. The file size of the combined MPEG-2 file was 59,779 KB.)
Stats of the AVI file after video compression, but with audio set to "direct stream copy".
Total file size: 74,712 KB
Video--
Data rate: 63 kbps
Audio--
Data Rate: 1536 kbps (while the original was 224 kbps!)
again sampling 48khz, stereo 16 bit
here is the clincher-under "Audio Tag":
"Tag: 0x0001, Not decodable
Microsoft PCM Format
PCM (uncompressed)"
So, apparently the audio coming out of "Direct Stream Copy" was not the same coming out as going on, but had been totally uncompressed. Does anyone know what that tag means?
Thinking that perhaps there was something about the original audio that was non-standard, that caused a problem for VDubMod, I decided to demux and transcode it. Using TMpgenc, I demuxed the mpeg-2 clip mentioned above. The resulting .mpv file was 47,877 KB, and the .mpa file was 10,390 KB.
I then transcoded the .mpa file with BeSweet (using the BeSweet GUI), to one of the presets, to create .mp3 audio at 128 kbps.
The resulting MP3 file was 5,935 KB in size. I then muxed it with the .mpv file using TMPGENC. The resulting .MPG file was 54,497 KB in size, a little smaller than the original (before transcoding the audio) 59,779 KB.
I loaded the new version of the MPEG-2 clip (with the BeSweet transcoded MP3 audio) into VdubMod. Properties shown-video same as original clip--1032 kbps. Audio 48khz joint stereo, 128 kbps layer III. And of course--file size-- 5935k.
I once again set it to save to AVI--exact same video settings as before, and again audio--"Direct Stream COpy".
Once more--resulting AVI with video much more compressed ends up much larger in file size than the original MPEG-2 file, 74,598 KB.
Its properties:
video data rate, same as other AVI (video compression was the same),63kbps.
Audio-also exactly the same as the other AVI, data rate 1536 kbps, `same tag, "not decodable", etc.
------------------
What is causing this problem? What is causing the "direct stream copied" audio to end up much larger than the original? What does that tag mean? Why "not decodable"?
I would appreciate any input anyone can give me into this problem.