Bitrates: DVD vs Bluray

[wayrus]

Hi, i'm no expert in the matter so i wanted to ask this question to get advices:
what is the technical (quality) difference between one bd 576p rip and one dvd5 rip, given that the bd has less or more half the average bitrates of the dvd? still the bluray should be better in terms of quality... isn't it?

thanks, have a good day.

[redwudz]

A quick guess would be that since they use different codecs and AVCHD on a BD is more
efficient than MPG2 on a DVD at the same or similar bitrate.

But other members here can probably answer your specific question.

And welcome to our forums.

[jagabo]

the bluray should be better in terms of quality... isn't it?

No. It depends on the codecs and settings used.

[Hoser Rob]

the bluray should be better in terms of quality... isn't it?

No. It depends on the codecs and settings used.

Beat me to it ... the settings are complex. I have seen x265 encoded video that had a pretty high bit rate but the quality was awful. Frankly I could have done a better job with xvid at the same bit rate, and I am no expert.

[wayrus]

thanks for the precious replies. how can i make a codec comparison between the two? i'm talking of a x264 encoded bluray by the way. i can also post the reports or specifics.


i'm thinking that in the end it all depends on the comparison of the MPEG-4 AVC (H.264) and MPEG-2. can mpeg4 beat mpeg2 at almost half the bitrates of the latter?

[manono]

It depends on the settings, as you've already been told twice. Use your eyes to determine which looks better to you.

[jagabo]

can mpeg4 (AVC) beat mpeg2 at almost half the bitrates of the latter?

If done correctly, yes. Maybe even one quarter the bitrate.

[hello_hello]

Using a PAL DVD as a source, most of my x264 DVD encodes would come in at well under DVD5 size (in the 2GB range with AC3 5.1ch audio) and should look as good as a DVD5 mpeg2 encode. There's generally not any complex encoder settings or tweaking to worry about. Mostly you'd use one of the default x264 speed presets and pick a quality (CRF value). If you encoded a PAL 16:9 DVD with x264 at 1024x576, and encoded a movie from Bluray after resizing down to 1024x576, and the encodes were both around the same size, you'd kind of hope the Bluray encode would look better though, given the Bluray source should have been better quality to begin with.

There are a lot of variables. Different videos require different bitrates to compress to the same quality (it depends how noisy the video is and how much action etc) so for x264 the encoding method might make a difference in respect to quality. When using it's CRF encoding method you'll see a CRF value in the encoder settings if you check them with MediaInfo. Something like:
rc=crf / crf=18.0
The CRF value chooses the quality but you have no control over the bitrate or file size. CRF18 is fairly high quality (the lower the CRF value the higher the quality)
For 2 pass or average bitate encoding you'll see something like this:
rc=2pass / bitrate=2500
or
rc=abr / bitrate=2500
That means a bitrate/file size was chosen for encoding, which determines the quality, but you have no idea what the quality will be beforehand. Therefore an encode of movie A at 2500kbps might look great, but for movie B it might look fairly average. There's no way to tell without looking at it for 2 pass or ABR encoding, whereas for CRF encoding the CRF value at least gives you some indication as to the quality to expect. That's quality relative to the source quality though, not quality as a whole. A CRF18 encode of a crappy source will still look crappy, whereas a CRF18 encode of a quality source should look quite good.

Still, If I had to choose a rule of thumb for quality, I'd generally assume a Bluray encode at 576p is going to look just as good, if not better, than a DVD5 DVD/mpeg2 encode of the same movie, even at half the bitrate, because the Bluray encode was probably a better quality source and h264 is a lot more efficient than mpeg2, but there really is no rule as such.

[wayrus]

thanks guys and gals you for your impressions, they are really useful to me. so now i get it much better, the final step i'm going to take is to compare the two rips of the same movie (from dvd source and bluray source) and i will post the specifics here.

i was using gspot for reading technical details but it turned out it doesn't read mkv files. too bad. suppose i will go for mediainfo..

[jagabo]

I don't think you really get it.

Starting from the same source, and encoding with the same frame size, frame rate, etc. an h.264 encoding can look better than MPEG 2 at the same bitrate. h.264 at 1/2 or even 1/4 the bitrate can look better than MPEG 2.

On the other hand, an MPEG 2 video at 720x400 might look better than h.264 at 1920x1080 with both at 4000 kbps, even if both start with the same high quality source. Because bigger frames require higher bitrates to maintain quality.

Or, what if the Blu-ray disc was made by upscaling a VHS source, whereas the DVD was made from a good clean film print. Nothing is ever going to make an h.264 encoding of that BD look good, even with 10 times the bitrate of the DVD.

So everything depends on the specific sources and properties of the encoded videos. You can't just make a blanket statement that MPEG 2 requires X times the bitrate of h.264. Whatever you determine from your two sources will only apply to those two sources and how you treat them.

[manono]

I think there's probably at least one more factor and that is these are both likely downloaded 'sources' and the competence of the encoder and the settings and filters used also come into play. Which is one reason I think this exercise is a waste of time and why I said for him to use his eyes to judge which he prefers.

[jagabo]

Yes, questions like this usually come from someone who wants to know which video he should download, rather than downloading both and deciding for himself which is better.

[manono]

Oh, right, and I hadn't thought of that possibility - that he really wants to know which he should get. I'd say there's no way to know in advance, although, all things being equal, x264 from a Blu-Ray source at half the bitrate of the MPEG-2 from a DVD source might be the better choice. All things being equal, which they rarely are.

[wayrus]

A CRF18 encode of a crappy source will still look crappy, whereas a CRF18 encode of a quality source should look quite good.

copy that. my movies are in fact encoded with 2pass.

[wayrus]

Yes, questions like this usually come from someone who wants to know which video he should download, rather than downloading both and deciding for himself which is better.

i was in need to ask that question because i can't tell a difference between the two and then i'd like more to save space on the hard disk rather than have a little difference in quality with a much bigger waste of space.

[wayrus]

http://www.streaminglearningcenter.com/articles/h264-vs-mpeg-2-quality.html

this might also be helpful!