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Re-coding HTDV to DVD file sizes?

544 Views 3 Replies 3 Participants Last post by  thymej
Can someone explain to me why one re-encoder makes a converted .ts file to .vob half the size when using all the same parameters: bit-rate=9.7M, res=720x480, AR=16:9, [email protected]&384bit-rate?

Using SuperC (GUI for FFMpeg) and setting it to the above parameters, a 45sec .ts test file re-encodes to a VOB size of 18MB.

Using HDTV1DVD (cant set the parameters but they happen to be the same as above except HDTV2DVD makes the bit-rate=7.8M. The same 45sec .ts test file is 40-45MB.

With the same parameters except for the bit-rate, why would a high bit-rate with FFmpeg make a smaller re-encode vob file then the lower bit-rate vob of the HDTV2DVD? I thought bit-rate was like the quality of the video?

What am I missing, am new here to this re-encoding stuff

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bit-rate determines file size too. More bits = higher quality (in general) = bigger file.
First off, 45 sec is not really long enough to let the rate control algorithms in most encoders properly work. If memory serves, Doom9 would always encode at least 5 minutes of video for his evaluations.

Second, the encoding parameters you speak of are max bitrate. The encoder will use less bitrate if it feels it is satisfied the "qaulity requirements." These quality requirements are set by the quantizer matrix used.

Also, I don't know about the settings for the first one you discribe, but HDTV2DVD uses 1 pass encoding. That, in combination with the very short length of the clip could very well be responsible for the in-acurate datarate.

Be aware that the explination about quantizers has been simplified to the point that it really isn't accurate. For a better understanding of how it all works, I suggest you do some surfing in the www.doom9.org forums. There really isn't a better place, for the average guy to learn about mpeg encoding software, in the world.

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BTW, I used a 45sec clip just to test many compos fast. I first noticed it when converting a 43min show. With SuperC it ended up with 1 1gb VOB and a 0.4gb, with HDTV2DVD is ends up with 2 1gb vob and a 0.4gb.

Also, the SuperC convetion does not seam to work well. Out of 6 standalone DVD players, only 1 can play it without slow downs and chuppyness. Its like I was trying to play a HD show on a PC that could not handle HD.

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