MPG2 Question

[nunorlima]

Hi!
I don't know if this is the right place for my question, but this is my first post in the community!
I have a simple question, a client of mine asked me to make some MPEG2 with the following specs:

VIDEO
Format: MPG2
Bit Rate Mode: Constant
Bit Rate: 30.0 Mbps
Resolução: 720x576
Acpect Ratio: original
Frame Rate: 25fps
Chroma SubSampling: 4:2:2
Scan Type: Interlaced
Scan Order: Top Field First

AUDIO
2 Stereo Channels
Mpg Audio Layer 2
Bit Rate Mode: Constant
Bit Rate: 224Kbps
Sample rate: 48kHz
Bit depth: 24 bits

Easy right? Wrong! I'm working on Premiere Pro CC and the only thing that I can't do is converting the audio to 24 bits. I've tried other converters (Xilisoft, MainConcept, Carbon Coder...) and in none of them I can chose the bit depth. I've also already read the MPEG sheet on the MPEG website and it doesn't even refer bit depths.
I'm starting to think that was a typo from the client...
Anyone knows if it's possible to make a MPG2 with 24 bits audio?

Thanks in advance!

[Keyser]

The 24 bit depth is probably reffering to the video. And 30 Mbps is way way too much for MPEG2.

[nunorlima]

But do know if it's possible to make a MPG2 with 24 bit audio? Thats my only problem...
On Premiere Pro CC I can do 30 Mbps, thats not a problem (and if the client wants that and I can do it i'll deliver that way)
Thanks!!!

[julitomg]

Well...if you really must work with these odd specs, you can export from Premiere, select only the audio, and open the resulting mp2 file in an audio editor (like Audacity for example) that allows you to change its bit depth, save it and then re-mux the audio file with your video file (m2v) rendered from Premiere (specifying separate streams and deselecting audio when exporting) I haven´t tryed anything like you describe but this way it could work (at least for your clients)

[nunorlima]

hummmm, that's a strange solution... my audio files are already bounced from pro tools at 48K-24bit. it makes no sense to me to convert to 16bit and then reconvert to 24bit... I can talk to my client and tell then that's a thing that it's impossible to do. as I said, it could be a typo when they wrote the specs...
thanks!

[Lowlander]

I haven't found the faintest of hints that resolutions other than 16-bit are even defined for MPEG-1 Audio Layer II (mp2) or MPEG-1 Audio Layer III (mp3). I'm pretty sure there is no such thing as a 24-bit mp2 (or mp3).

Audacity for instance does only allow for bitrate adjustment as the only option when exporting to mp2. Regardless of the project's actual sampling depth, the output is always 16-bit.

[nunorlima]

I'll explain better:
my client sent me some MXF files. I did the audio post on pro tools and bounced to a wav 48k 24bits. Then i'm supposed to make some cuts on the video and export to MPG using the specs that I posted on my first post. But the only thing that I can not do is exporting an MPG with 24bits audio.
I'm starting to think that the MPG norm as some kind of limitation regarding 24bits audio and the client made a typo when writing the specs...
Does anyone can help? I've read the MPG norm and it does not say nothing on 16 ou 24bits...
Thanks!

[pandy]

The 24 bit depth is probably reffering to the video. And 30 Mbps is way way too much for MPEG2.

Not for for HL - up to 80Mbps is ok for MPEG-2.
https://en.wikipedia.org/wiki/H.262/MPEG-2_Part_2#Video_profiles_and_levels

[nunorlima]

Thanks for the reply Lowlander!

[pandy]

I'll explain better:
my client sent me some MXF files. I did the audio post on pro tools and bounced to a wav 48k 24bits. Then i'm supposed to make some cuts on the video and export to MPG using the specs that I posted on my first post. But the only thing that I can not do is exporting an MPG with 24bits audio.
I'm starting to think that the MPG norm as some kind of limitation regarding 24bits audio and the client made a typo when writing the specs...
Does anyone can help? I've read the MPG norm and it does not say nothing on 16 ou 24bits...
Thanks!

In your case audio must be compressed with MPEG 1 Layer II codec (a.k.a. MP2).
Also to have 4:2:2 you must use at least something like '422P@ML'.

[nunorlima]

Yes, pandy. My only problem is with the audio specs. 30Mbps on the MPG is piece of cake.

[pandy]

I haven't found the faintest of hints that resolutions other than 16-bit are even defined for MPEG-1 Audio Layer II (mp2) or MPEG-1 Audio Layer III (mp3). I'm pretty sure there is no such thing as a 24-bit mp2 (or mp3).

Audacity for instance does only allow for bitrate adjustment as the only option when exporting to mp2. Regardless of the project's actual sampling depth, the output is always 16-bit.

MP2 or MP3 have no internally defined bits - it is discrete time/level function but level can be described with accuracy higher than 16 bits for sure (depends from implementations maybe 20 - 22 bits are possible).
So easily as a result of MP2(MP3) decoding 24 bit PCM files with 20 - 22 bits resolution (dynamics) are possible.

[nunorlima]

but pandy, even with MPEG 1 Layer II codec i can not chose between 16 or 24 or 32 bits. and the wiki page on MPEG 1 Layer II codec only makes reference to bitrates and sampling rates...

[usually_quiet]

I'm starting to think that the MPG norm as some kind of limitation regarding 24bits audio and the client made a typo when writing the specs...
Does anyone can help? I've read the MPG norm and it does not say nothing on 16 ou 24bits...
Thanks!

I had the same experience. The only references I found using Google that mentioned 24-bit audio were for PCM, Dolby TrueHD, and DTS. Most of the articles I looked at said nothing about bit-depth for MPEG-1 Layer 2 audio. I found a single reference for DVD audio that mentioned 16-bit MPEG-1 Layer 2 audio.

[newpball]

I do not see the problem with 24 bit PCM.

[nunorlima]

I had the same experience. The only references I found using Google that mentioned 24-bit audio were for PCM, Dolby TrueHD, and DTS. Most of the articles I looked at said nothing about bit-depth for MPEG-1 Layer 2 audio. I found a single reference for DVD audio that mentioned 16-bit MPEG-1 Layer 2 audio.

yep, me too...

[poisondeathray]

Just double check with your client

[nunorlima]

I do not see the problem with 24 bit PCM.

me neither! but the client asked for MPEG Layer 2, not PCM or even AAC..

[Cornucopia]

What pandy is trying to say is that DCT/FFT-compressed formats like mp2 are internally bit-depth agnostic - there is no way to specify the internal bit depth, because internally the file is just made up of bitrate quantizer coefficient blocks. While it MAY be possible with some encoder apps to designate the "original/intended" bit-depth, this is by no means universal, and doesn't affect how most decoders will attempt to decode the file.
So, let THEM (your client) worry about the decoding. If you start with a high quality 24bit uncompressed source and properly encode it to the suggested bitrate and sample rate using a good mp2 encoder, you will have done your job. If the client has a 24bit-capable decoder, they'll get a 24bit LPCM stream out of it, if they don't, they'll get a truncated-to-16bit LPCM stream out of it.


Also note: there is no designation in MPEG video for "Original" aspect ratio. It should be an actual numbered ratio here (4:3, 16:9) and should be referring to Display (Frame) AR. If the client wrote this as shorthand to suggest you not change the AR and just pass it through from its source, do so, but it should be designated anyway. If that wasn't their intention, this also was a typo.

You should also get clarification as to whether you should provide this MPEG muxed as a PS stream file or a TS stream file (or MP4 file or MXF file).

Scott

[nunorlima]

Thanks a lot Scott!!! that was very helpful!!!
Yes, I forgot to say that the client wants a MPEG-PS and the "Original" aspect ratio is 16:9. But I didn't mention this because my only problem was with that piece of information regarding the 24-bits audio. All the other specs i sorted out on AME.

[pandy]

Yes, pandy. My only problem is with the audio specs. 30Mbps on the MPG is piece of cake.

Assumption is that your source is 24 bit (in this way i understand requirement) and sad info for you - i made quick test and seem that twolame library is somehow limited in ffmpeg to 16 bits... (i tested this and seems that decoding of the MP2 in LibAV is only 16 bit - sad...) not sure about MP2 codec implementation in your software.
And as i said previously - MP2 internally have no bits rather quantization steps and limited function resolution (coefficients).

[pandy]

What pandy is trying to say is that DCT/FFT-compressed formats like mp2 are internally bit-depth agnostic - there is no way to specify the internal bit depth, because internally the file is just made up of bitrate quantizer coefficient blocks. While it MAY be possible with some encoder apps to designate the "original/intended" bit-depth, this is by no means universal, and doesn't affect how most decoders will attempt to decode the file.

Yes, generally this is what im trying to say with one remark that mp2 is not DCT/FFT based codec - however principle is exactly same as DCT/FFT. Thx Scott.

[Cornucopia]

My mistake. MP3, AC-3, DTS, AAC, etc are DCT/FFT (frequency-domain)-type codecs, but MP2 (along with MP1) is a sub-band (time-domain) codec. Rest still applies.

Scott

[nunorlima]

Thanks to you all! You've been very kind! 😃 tomorow i'll talk to my client and expose those facts.
Kind regards to you all!

[nunorlima]

Hi!
Today my client replied to me and said that the 24bits MPEG audio was a mistake that they made when writing the specs...
Thanks again to you all for the help!