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Sansa clip+ : half pitch

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porjo:
Player is Sansa Clip+ with Rockbox 3.13 firmware

I regularly convert mp4 files from Youtube to m4a using MP4Box command line utility e.g.


--- Code: ---$ mp4box -add audiofile.mp4#audio audiofile.m4a
--- End code ---

Occasionally I find that the pitch of the audio is too low when played back on the Sansa Clip. If I adjust the pitch to 200% the audio sounds normal.

An example file that exhibits this problem is as follows:


--- Code: ---$ mp4box -info audiofile.m4a
* Movie Info *
Timescale 600 - Duration 01:52:44.808
Fragmented File no - 1 track(s)
File suitable for progressive download (moov before mdat)
File Brand M4A  - version 1
Created: GMT Thu Oct 24 13:15:06 2013

File has root IOD (9 bytes)
Scene PL 0xff - Graphics PL 0xff - OD PL 0xff
Visual PL: No visual capability required (0xff)
Audio PL: High Efficiency AAC Profile @ Level 2 (0x2c)
No streams included in root OD

iTunes Info:
Name: Audiofile

Track # 1 Info - TrackID 1 - TimeScale 44100 - Duration 01:52:44.808
Media Info: Language "Undetermined" - Type "soun:mp4a" - 145668 samples
MPEG-4 Config: Audio Stream - ObjectTypeIndication 0x40
MPEG-4 Audio MPEG-4 Audio SBR - 2 Channel(s) - SampleRate 22050 - SBR SampleRate 44100
Self-synchronized

--- End code ---

My guess is that the Sansa is playing 22khz auido at 44khz sample rate (does that make any sense?)

Does anyone know a) why this is happening b) what can be done to fix the issue (without modifying pitch on the player)?

saratoga:
It does sound like the SBR part isn't decoded correctly resulting in half the sample rate.

Do the files decode correctly in other software?

Echo:
Is this just the pitch that is different or also the sound is playing slower? (should be twice as long or cut somewere in 50% of the sound original length)
If it dose that it is most likely bitrate issue and may even be fixed manually, depending on the exact format.
If not then it is very, very strange.

I also noticed that the track has 2 channels. Maybe the nono/stereo definition is incorrect?
Try looking at all your problem files and see if they all stereo.
That check all your good files and see if they all mono.
If so than that may be case.

Good luck

Julian67:
This looks the same bug as FS#12856

silvertree:
I encountered this phenomenon last night from the same circumstances.

I used last night's build on Sansa Fuze+

I downloaded some youtube .3gp content and demuxed the audio with YAMB.

The 2 troublesome tracks were 32kkps AAC.

Here's what mediainfo had to say about both of the problem files:

Audio
ID                               : 2
Format                           : AAC
Format/Info                      : Advanced Audio Codec
Format profile                   : LC
Codec ID                         : 40
Duration                         : 11mn 8s
Bit rate mode                    : Variable
Bit rate                         : 32.0 Kbps
Nominal bit rate                 : 236 bps
Maximum bit rate                 : 35.2 Kbps
Channel(s)                       : 1 channel
Channel positions                : Front: C
Sampling rate                    : 22.05 KHz
Compression mode                 : Lossy

[edit] I just mentally processed echo's question: the files are low pitch as a result of playing slower.

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