Re-Encoding AC3

[EpheMeroN]

Is there a tool that can tell me all specs about an AC3 file so I can know what info to enter into an encoder such as Aften for re-encoding?

I usually use delaycut to give me the basics, but I notice Aften has settings for things such as DPL and DRC and I'd like to know what the original file's info was to be re-entered.

[tebasuna51]

Is there a tool that can tell me all specs about an AC3 file so I can know what info to enter into an encoder such as Aften for re-encoding?

I usually use delaycut to give me the basics, but I notice Aften has settings for things such as DPL and DRC and I'd like to know what the original file's info was to be re-entered.

The DRC type applied can't be know because is not in BitStreamInfo part of frame header, is a dB value (+/0/-) to apply (or not) by the decoder, in each audio data block.

BTW you can try this tool (without guarantee): LeeAudBi (http://www.sendspace.com/file/f1aiwe)

Dolby Surround Mode is detected (only a flag, can be true or not, without difference beteen DPL or DPL II)

You have 3 settings for ac3 info:

- 'Only first frame': quick full info about first frame and 'Estimated Info' about the whole stream.

- 'Extended info' (default): full info about first frame and 'Revised Info' about the whole stream. Slow because all frames are revised to detect errors. A line info is generated for each problem (uncomplete frame, different basic parameters, ...)

- 'More Complete Info': full info about first frame, 'Revised Info' about the whole stream and a line info for each frame. This line contain the DRC value for the first block (there are 6) in the frame. Warning when use with big files.

The only way I know to detect the DRC type is:
1) Select a little fragment of original ac3 file and analize with Complete Info.
2) Decode to wav without DRC, DialNorm, etc.
3) Encode to ac3 with different DRC and same DialNorm to match the original (Complete Info)

Warning, all encoders introduce 5.333 ms of delay (first block padded with silence) then you must cut the first 5.333 in wav file (second pass) or use -pad 0 with Aften.

EDIT: Corrected a little bug in LeeAuBi 'More Complete Info' option.

With 'Extended Info' Dyn. Range min/max data also can see the DRC option than match.

Edit: New link and version LeeAudBi03b.7z (http://www.sendspace.com/file/7izmtk)

[EpheMeroN]

Thanks for the nice little app! I'm playing with it right now.

Btw, if AC3 encoders like Aften always introduce 5.3ms of audio delay why isn't it auto-corrected in the application itself?

[tebasuna51]

Btw, if AC3 encoders like Aften always introduce 5.3ms of audio delay why isn't it auto-corrected in the application itself?

The first block can't be encoded properly if contain audio info, then the choice is introduce a first block with silence instead deform the first audio data.

Here is important because the tool only read the DRC of first block in frame, if was delayed 5.33 ms the first block in original ac3 now is the second.