Use Main Profile@3.0; 3.1 or Hight Profile@ L4.1 [Archive]

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vfx3love

17th August 2012, 11:48

Hi All,

I'm try use OBE transcoding for liveTV. But I dont know choice right format profile config get best quality. My video target Mp4 bitrate 2,5Mbps; SD resolution: 720x576.

One guy recommend me use High Profile@L4.1 better than Main profile@L3.0 or L3.1 because High Profile had feature more than Main profile ( him send me wiki link to prove it) and commitment video target get superior quality. This right ? Sorry my english not good.

LoRd_MuldeR

17th August 2012, 12:37

H.264 Profiles and Levels are two different things:

The "Profile" of a H.264 stream is determined by the encoding features that have been used in the creation of that stream. If any "High" profile features have been used, the stream will come out as "High" profile. If only "Main" profile (and below) features were used, the stream will come out at "Main" profile. If only "Baseline" features were used, the stream will come out as "Baseline" profile. And so on.

There are some "High" profile features (such as "8×8 vs. 4×4 transform adaptivity") that certainly improve the compression ("quality per bit" ratio), so you normally do want to use these. But it all depends on your playback device! If your playback device is restricted to "Main" profile, it cannot play "High" profile streams. In that case you are forced to restrict yourself to "Main" profile. If your playback device does support "High" profile, you can (and probably should) use the "High" profile features.

As for H.264 "Levels": The Levels impose restrictions on the maximum "resolution @ framerate" supported. So the "Level" at which your H.264 stream will come out is determined by the resolution and framerate of your source video. If the playback device doesn't support the required Level, you will have to downscale the video to a smaller resolution - and thus reduce the required Level to what is supported by your playback device. The number of reference frames you can use (at a specific resolution) is also restricted by the Level; or more specifically by the maximum DPB size.

vfx3love

19th August 2012, 14:14

Thank your so much.

Late time, I think SD video with bitrate~2Mbps (for KPI DVB Broacast) only use Main profiles .

Because I read some topic compare Main profile and High profiles, they say use High profile for SD video had low bitrates no effect. They wrong ?

If my STB can playing HP, I need choice HP for better quality, right?

Sorry for more question, Many thank for help .

LoRd_MuldeR

19th August 2012, 14:39

Because I read some topic compare Main profile and High profiles, they say use High profile for SD video had low bitrates no effect. They wrong ?

That's the wrong way to think about Profiles. You don't "use" a Profile. You use features that may (or may not) be allowed under a specific Profile.

Again: An H.264 Profile just defines which encoding features of H.264 are allowed and which are not. In "High" profile some additional and more sophisticated encoding features may be used that are not allowed in "Main" profile. At the same time, "Main" Profile allows some feature that are not allowed in "Baseline" Profile. And so on... There even are some features only allowed in lower Profiles, but these are "exotic" and can be ignored here.

Therefore, when your H.264 encoder is making use of more "advanced" encoding features, the resulting H.264 stream will come out at a higher Profile. For example, when "8×8 vs. 4×4 transform adaptivity" is used, then the stream comes out at "High" profile, because "8×8 vs. 4×4 transform adaptivity" is a "High" Profile feature. Thus, if you need to stick with "Main" Profile, you cannot use "8×8 vs. 4×4 transform adaptivity".

Using more "advanced" encoding features can improve the "quality per bitrate" ratio. Thus you might be able to improve the quality at a given bitrate. But, at the same time, by using encoding features that need a higher Profile, you also restrict the playback devices that will be able to play your stream. For example, a "High" Profile stream requires a "High" Profile capable player. A player that only supports "Main" Profile, cannot play "High" Profile streams.

That is no different between HD or SD content! However when compressing HD content and bitrate is scarce, the improvements you can get form using "High" Profile features (as compared to restricting yourself to "Main" Profile features) may be more important than for SD content. Nonetheless there is absolutely no reason why "High" Profile would be any worse for SD content.

For more details, please have a look at the Wiki article:
http://de.wikipedia.org/wiki/H.264#Profile

If my STB can playing HP, I need choice HP for better quality, right?

If your playback device supports "High" Profile (and you don't care about other playback devices), then I see no reason why you would not want to make use of "High" Profile features...

vfx3love

19th August 2012, 18:31

Thank so much. Now I understand !:thanks:

kieranrk

20th August 2012, 01:03