MP4 to MP3 conversation (Video+Audio -> Audio)

[Vangelis forthnet]

On Thu Aug 29 00:32:47 BST 2013, Kris Szajdzicki wrote:

>Thank you Shevek for your suggestion (ffmpeg -i file.mp4 -vn -q:a 2
>file.mp3).
>This runs, but the screen is filled with red error messages.
>I tried it with both MP4 & WMV files with no difference.
>Could it be due to DRM or something similar - I know that the BBC are
>protective of their output
>Attached is the MP3 output and screen dumps of the start & end of the
process.

Hello Kris!
If Shevek would kindly allow me to step in, then:

>Input #0, mov,mp4,m4a,3gp,3g2,mj2, from
>'F:\BBC_iPlayer\repository\NK_4S.mp4':
>Metadata:
>major_brand     : mp42
>Duration: 01:29:02.12, start: 0.000000, bitrate: 1510 kb/s
>Stream #0:0(eng): Video: none (encv / 0x76636E65), 832x468, 1407 kb/s, 25
>fps, 25 tbr, 25k tbn, 25k tbc
>Stream #0:1(eng): Audio: aac (enca / 0x61636E65), 24000 Hz, stereo, fltp,
>99 kb/s

 From the info above produced by FFmpeg I can tell that you are trying to
process an encrypted MP4 file (encv=
encrypted video stream, enca= encrypted audio stream), most probably your
MP4 file "NK_4S.mp4" came from
the official iPlayer Desktop App (that uses Adobe Air) and downloads DRM'd
files.
 Likewise, the wmv files downloaded from a programme's iplayer page are also
DRM'd - DRM'd files (be they MP4
or WMV) cannot be converted to anything else - they play in the designated
player (iPlayer Desktop / Windows Media
Player) for as long as the DRM lic allows, then they expire and are nothing
but junk bytes...
 I may be walking on treacherous territory now, but if it's only the audio
part of the files you are after, then there exist
methods of saving the audio stream as it is being played back by the DRM
capable player by accessing your sound card
analog audio output and converting that to a lossy format (e.g. MP3) - but I
won't be providing any more info... !
Let me state it clearly, I DO NOT ENDORSE DRM CIRCUMVENTION!

On Sun Aug 25 23:29:24 BST 2013, Shevek wrote:

>There is no DRM in the downloaded video.

 Kris, this is indeed true for the MP4 video files recorded by Get_iPlayer.
So, you must find the TV programme that your DRM'd file NK_4S.mp4
corresponds to and download it using Get_iPlayer this time (provided it is
still
available on the iplayer site - else you are out of luck, I'm afraid...)

Now, the audio part of 95% of the Beeb's MP4 video files in flash(v)high
& flashhd tvmodes is actually encoded in HE-AACv1 @ 96 kbps ABR
(HE-AACv1 = AAC-LC + SBR) - as already stated by Shevek, this can
be losslessly extracted from the MP4 container using FFmpeg:

ffmpeg -i "DRM-free-tvfile.mp4" -vn -f ipod -c:a copy -bsf:a aac_adtstoasc
"audio-only.m4a"

or, if you are familiar with it, MP4Box can also do the job brilliantly:

MP4Box -raw 2 "DRM-free-tvfile.mp4"
MP4Box -add "DRM-free-tvfile.aac:name=HE-AAC Audio
Stream:lang=en:sbr:mpeg4:ipod" -itags tool=MP4Box -new "audio-only.m4a"

If your software/hardware player supports playback of m4a files, you should
stick to those!
Else, if you must transcode, use FFmpeg as already suggested -
if I may say so myself, transcoding from HE-AACv1 @ 96 kbps ABR to
MP3 -V 2 (= 170...210 kbps VBR) as proposed is a bit of an overkill...
I personally find that using CBR @ 128kbps is adequate for most cases:

ffmpeg -i "DRM-free-tvfile.mp4" -vn -c:a libmp3lame -ab 128k -ar 44100 -ac 2
"audio-only.mp3"

I do hope you get your issue resolved!

Cheers,
Vangelis.