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SBR detection/playback, How to verify SBR flag? How can I be sure player gets it right ?
post Jun 15 2012, 12:43
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Hi. I need to solve two - somewhat related - questions regarding detection and playback of AAC files with SBR:

(1) How can I verify whether an AAC file uses SBR and whether the SBR flag is set in the container ?

According to https://trac.bunkus.org/ticket/757 the raw AAC audio stream does not communicate whether or not it has SBR, instead this info is stored as a flag in its container. I manually set/unset the SBR flag in (in this case) the Matroska container, but this did not change the MediaInfo output at all, so either un/setting the SBR flag did not work OR MediaInfo ignores the container's SBR flag and directly analyzes the raw AAC audio stream similarly to what the coder of MKVtoolnix claims his tool does:

QUOTE ('Moritz Bunkus')
mkvmerge detects whether or not the source contains SBR. In the case of raw AAC files this may be wrong because the container itself doesn't provide a hint. Therefore mkvmerge employs heuristics (it guesses).

In the first case how can I set/unset the SBR flag?
In the second case, what tool can tell me the container's SBR flag status ?

(2) How can I acertain whether or not the player takes account of and uses SBR ?

I wanted to create a file which claims to have SBR but actually doesn't OR a file which doesn't have SBR but erroneously claims to have it
-> in order to compare playback of such file to the source file (same raw audio content but with correct SBR flag). I don't have fine hearing, but I thought the difference must be so obvious, that I could hear it. Unfortunately I wasn't able to produce such a file, as can be seen in the link above.

Can someone help me create a scenario, where I can hear the wrong playback and compare it to how the playback should sound like (when correctly using SBR) ?

Many thanks

This post has been edited by chrizoo: Jun 15 2012, 12:50
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