Created MP3 problematic from custom software

Tell

Member
Can I report that the MP3 file produced by the custom software via the MP3 option on the decrypted file isn't uniformly playable. Whilst the created file plays fine within Vista using Winamps, a Denon Media Player doesn't. Running it through Xilisoft conversion MP3 to MP3 does play, so I'm left thinking that the software needs slightly different options set on the custom software that produces the MP3 files.

Happy to supply these files to anybody to look at if you give me an area to put them in [before and after]. It's 75 minutes off the Archers although one suspects it can be replicated on something smaller.
 
OP
T

Tell

Member
Thanks Black Hole

Reading that I'm still of the view that the industrial standard package being called just needs the parameters twigged to make it work correctly. After all it is this package that many if not all of the commercial tools use.

FFMPEG
 

Ezra Pound

Well-Known Member
The Humax does not have the CPU power required to convert files to the 'standard' MP3 format, it does have enough power to extract the MP3 audio in the format it is already in from the video/ audio TS stream. So although it would be possible to change the ffmpeg parameters when extracting the audio, the Humax would not be capable of running in this mode. The following will convert to the 'standard' MP3 format BUT, it is not practical to run this while the Humax is also being a TV tuner
Code:
ffmpeg -i input.ts -vn -ar 44100 -ac 2 -ab 192000 -f mp3 out.mp3
 
OP
T

Tell

Member
Thanks. I'll have to have a look at that.

The odd pause in normal operation to generate one file one would think would not be an issue unless it threatened background operation of any material being recorded. Not faffing around with a PC has many advantages.
 

Black Hole

May contain traces of nut
You can dedicate all the processing power of the Humax to the problem by booting into maintenance mode via the Telnet menu. EP tested the ffmpeg process when we were discussing this before, and it runs... very slowly.

I have processing power to spare - three HDRs which mostly sit around doing nothing. I would be very interested in having a "magic folder" where I could drop a radio .ts (or the mp2 extracted from a radio .ts) and a proper .mp3 appeared some time (even days) later - although it would have to work without maintenance mode and suspend operation when the Humax was doing something else.
 

Black Hole

May contain traces of nut
So what do we need to do then? The best bet would be a WebIF auto option to tag a folder, with the ffmpeg process running at a really low priority. How would one know the job had finished?
 

prpr

Well-Known Member
The Humax does not have the CPU power required to convert files to the 'standard' MP3 format, it does have enough power to extract the MP3 audio in the format it is already in from the video/ audio TS stream. So although it would be possible to change the ffmpeg parameters when extracting the audio, the Humax would not be capable of running in this mode.
Yes it would be possible. It just runs very slowly.
The following will convert to the 'standard' MP3 format BUT, it is not practical to run this while the Humax is also being a TV tuner
Code:
ffmpeg -i input.ts -vn -ar 44100 -ac 2 -ab 192000 -f mp3 out.mp3
Yes it is practical. It just runs very slowly.
As long as you set the priority of the background process to something low, then it won't interfere with normal operation.
Or perhaps you just don't understand multitasking operating systems?
 
OP
T

Tell

Member
Will have a look... I'd have you know that my first degree was in Mathematics and Computer Science - 1/3 computer science in the days of PDP 8s and PDPs 11 and ICL 1904s and IBM370s... punch tape and cards...

Now I'm sure there is something wrong with the documentation of the Wiki in the audio section and what this is all really about:

>>
Extract Audio

Web-If MAIN >> BROWSE MEDIA FILES >> (Select Single File) >> OPT+ >> Extract Audio
This function will produce an MP3 file containing the stereo audio track contained in a standard Def. Video file (or radio recording), The following conditions must be met :-
  • The file must be decrypted (Displays a DEC against it)
  • ffmpeg package must be installed
  • Standard Def. recording only (Hi-Def 2 Ch or 6 Ch sound won't be decoded)
  • The extracted MP3 file is an MP2 Layer 7 file (also called MP2 Audio), not the more common MP2 Layer 3, transcoding to layer 3 is not carried out due to amount of CPU usage required
<<

If we read MP2 Layer 7 to be shorthand for MPEG2 Layer 7 then that's AAC but that's only used for the HD transmissions. So that last bullet point is problematic. It also says it won't do AAC in any case. That last bullet point is wrong I would suggest it means Layer 2 ?.

Whilst the Denon site has this to say about it's equipment which will be what the hardware I was trying to play it on had problems:

>>
The AVR-5805/4806 is compatible with “MPEG-1 Audio Layer-
3” MP3 files (with sampling frequencies of 32, 44.1 or 48 kHz).
It is not compatible with “MPEG-2 Audio Layer-3”, “MPEG-2.5
Audio Layer-3”, “MP1” or “MP2” files
<<

I reckon we are talking about the source being MPEG-2 Audio Layer-3 and the software produces MPEG-2 Audio Layer-3 and calls it MP3 ?.

WINAMP sees it as:

>>
Payload Size: 116537934 bytes
Header found at: 1458 bytes
Length: 4855 seconds
MPEG-1 layer 2
192 kbps (VBR), 202323 frames
48000 Hz Joint Stereo

CRC: Yes, Copyrighted: Yes
Original: Yes, Emphasis: None
<<

So we need a layer 3 out of it.

Is this the case where the software is using the internal chip set to quickly produce the MPEG-1 Layer 2, but but doesn't produce the Layer 3 /MP3.

So we are led to believe that some MP3 player play MPEG-1 Layer 2 ?... so what that menu option produces isn't MP3 as it suggests but a codec that some players may be able to play.

http://en.wikipedia.org/wiki/MPEG-1_Audio_Layer_II
 

rpb424

Active Member
Correct, it's 'mp3' in the sense that some mp3 players will be happy with it, but not all. In reality it's mp2. There's really no feasible way of producing anything more compatible within a reasonable timescale due to lack of system resources.
 

Ezra Pound

Well-Known Member
Tell : Extract Audio . . .
I take your point that output file is not the more commonly used MP3 (Layer 3) configuration, however these files are accepted as MP3 and can be played by some MP3 players. It would be better if the output file was layer 3 but that would require conversion of the extracted MPEG-2 audio and this was deemed not possible due to lack of CPU free time.
I have re-worded the WiKi page as follows :-

"The extracted MP3 file is in a format sometimes called MPEG-2 audio, not the more common Layer 3 audio, although some MP3 players will accept this format, a greater number of MP3 players require the layer 3 format, transcoding to layer 3 is not carried out on the Humax due to amount of CPU usage required"
 
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