Two types of AMR:
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1.AMR or AMR_NB ( AMR narrow band) - Mono channels ( 8 bit audio)
2.AMR_WB ( AMR wide band) - stereo channels ( 16 bit audio)
we are using AMR_NB ;
Every AMR file begins with following Hex start codes:
23 21 41 4d 52 0a ( Equal string is: #!AMR.)
if we open the amr file, without these start codes means it will display like
---------------------------
Error
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Error -2048: Couldn't open the file Quotes.amr because it is not a file that QuickTime understands.
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OK
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Every audio frame is having one byte frame header;
format is as follows:
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F ( 1 bit) | FT( 4 bits) | 1 ( 1bit)
---------------------------------------------
Frame Type | Mode | Frame Size(Including 1 byte header) |
0 | AMR 4.75 | 13 |
1 | AMR 5.15 | 14 |
2 | AMR 5.9 | 16 |
3 | AMR 6.7 | 18 |
4 | AMR 7.4 | 20 |
5 | AMR 7.95 | 21 |
6 | AMR 10.2 | 27 |
7 | AMR 12.2 | 32 |
if we have a file with 12.2 kbps means, we can check this by the frame header;
and moreover we can note that every frame have 1 byte header;But it is same as start. Assume that first frame's header is 3C then every frame must begins with header start code ;
if the header is having proper start code and the next it will check whether every frame is having same header info; otherwise it will reports the error as follows:
"Quicktime media file is having incorrect duration"
I have to do one more check;
if every frame is having different header start code whether the QuickTime play that AMR file ?...
3C is a frame header for first frame;
38 is a frame header for second frame;
Both frame headers indicate the same Frame Type;
whether it will works ?
Result :
----------
it works fine;
Test case 2:
-------------------
Instead of 0x38, I inserted the 0x20.
Then I didnt get any sound while playing it in QuickTime player and moreover the Quicktime is not giving any errors;
Instead of 0x20, I made it as 0x20, then I faced the same problem.
Every AMR frame is having 20 ms of data;
So if 40 frames are available means
40 * 20 = 800 milli seconds( play time of that frames);
1000 milliseconds = 1 second
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