Repair Corrupted Audio File

How to fix corrupted voice memo (m4a) files. Do you have broken voice memo files? You can fix those files by yourself. I will show you the steps in this article. Voice memo files have the extension “m4a”. It is audio data encoded in the AAC format and encapsulated in MPEG4 file container.

Unsupported Browser

  • Re: How to fix a corrupt wav file? Try File - Import - Raw Data. You'll have to enter the correct bit-depth (and it should be PCM encoding), number of channels, and the sample rate. If you get 'pure noise', try incrementing the offset by one.
  • To fix the corrupted WAV file, enable the 'Repair audio length' option and click on the Repair button. Wait for a few seconds as the tool would repair the corrupt WAV file and improve its playtime. In the end, you can listen to the fixed audio file or just save it to your local system.

This page probably won't work great in Internet Explorer. We generally only support the recent versions of major browsers like Chrome, Firefox, Safari and Edge.

AAC is the audio encoding format that has become the standard for capture and delivery in consumer markets.

Music sold on the iTunes Store comes encoded in AAC format. iTunes encodes songs in AAC format by default.

At similar bit-rate, AAC achieves better quality than MP3 encoding.

Repair of corrupted AAC files

Fix Corrupted Audio Files

AAC is difficult to repair due to lack of headers in AAC frames.

AAC can be found in audio files, usually in QuickTime and MP4 files using the extensions .m4a .m4b .m4p .mov and rarely as raw streams in .aac .adif and .adts files.

Repair consists in reindexing the AAC frames into a .M4A / MOV file.

In video files, AAC is often used to encode audio. It is common to find AAC paired with H.264 or H.265 video formats .

Treasured can detect AAC in damaged audio files.

File

Since fall of 2018, at Aero Quartet we have observed a surge of requests to fix audio recordings made with an iPhone and Voice Memos app.

  • In iOS 12, Voice Memos app has a feature called Replace to edit an original recording.
    0010Replace is not reliable and can corrupt the original recording.
  • Corrupted recordings can be repaired, but are significantly shorter in duration than originals.
    The missing duration is lost forever.
  • The problem seems to have been solved in iOS 13.

Consult dedicated blog post for more information.

Our service offers:

  • FREE diagnostics and preview with Treasured
  • FREE sample of repaired video
  • Try before you buy with a FREE trial of your Repair Kit
  • Enjoy FREE customer support by speaking directly with our trained experts
  • Invaluable expertise, dedication and second to none customer service
AAC overtook
the most
popular
at the
turn
when iPods and iTunes
Repair Corrupted Audio File

AAC Repair Techniques

Repairing raw AAC data requires that each frame is identified, and then re-indexed or rewrapped into a playable container format. The hardest part is to identify AAC frames, since they don't have a header and have a variable length. Below we present 3 methods of increasing complexity, that produce respectively audible audio, audio with glitches, and good audio.

Pattern matching: This is an empirical method that doesn't try to validate AAC by the coding rules, but by patterns observed in the bitstream. Pattern matching uses bits matching, block lengths filters, ... With this simple technique, audio becomes audible, but quality is not good.

Surface decoding: This method decodes the beginning of an alleged AAC frame to validate it. It can check that important parameters — gain, maxsfb, frame size and termination — have coherent values. It achieves a good result, but not perfect, with one fault every 500 frames. We describe this technique in detail below...

Decode-Validate: This method, introduced in 2009, is giving near-perfect results. It uses a AAC decoder to validate alleged AAC frames. Frames that pass the test are then indexed and wrapped into the repaired M4A audio file.

Guidelines for parsing an AAC bitstream with 'Surface decoding'

AAC uses variable-length blocks that are difficult to parse and identify.

In most common case, stereo LC AAC, we'll have the following bitstream:


  • If common window is 0, we have a Multiple Window (see below)
  • If window sequence (2 bits) is 2, we have a 'EIGHT_SHORT_SEQUENCE' (see below)

Otherwise, the common case continues like this:


Repair Corrupted Audio File Online

maxsfb must be between 0 and the value from this table:


It's common in a given file to only see two maxsfb values: one for EIGHT-SHORT-SEQUENCE, one for the rest of blocks. maxsfb value is usually close to or equal to the maximum of the table.

  • Predictor should always be 0.
  • If mask (2 bits) is equal to 1, then between mask and gain we insert maxsfb bits.
    In EIGHT_SHORT_SEQUENCE case, this value is multiplied by the number of windows.
  • Gain is usually between 100 and 200, and usually does not vary a lot in a given file.

After gain, we have the scale factor data (sequence of 4 and 5 bits):


Repair Corrupted Audio File

We verify that after several sequences, summing the 5 bits increments, we arrive exactly on maxsfb (47 in this case).
Note that 5 bits increments should never be 0, and the 31 value triggers a new reading of 5 bits (example: 31, 5 gives 36)

EIGHT-SHORT-SEQUENCE

windows sequence is always 10 (2) in eight-short-sequence frames.


Note that here maxsfb is 6. Scale factor grouping with 2 zeros tells that we have 3 groups. Therefore, we have 3 sequences of alternate 4 and 3 bits that sum exactly 6.

Multiple Windows

This block has a different layout with 2 consecutive sets of data.


Just after predictor, we have the scale factor data (sequence of 4 and 5 bits).

Multiple Windows and EIGHT-SHORT-SEQUENCE

This combination is possible, and has the following layout:


Just after grouping, scale factor data starts (sequence of 4 and 3 bits)

Degenerated block

You can find very short blocks with no data:


Note the layout of the two windows (second window starts with gain)

Degenerated block with padding

You can find blocks that appear normal in size but that contain no data:


AAC mono

Starts with this:

Corrupted
Corrupted

External links

Repair Corrupted Wav Audio File

http://wiki.multimedia.cx/index.php?title=Understanding_AAC
http://getid3.sourceforge.net​/source/module.audio.aac.phps

Repair Corrupt Audio Files


Comments are closed.