The audio codec for mp4 atom

 

In the 'esds' atom there are a few fields of relevance to determining the codec used. The first byte of content of the esds atom is the objectTypeIndication. (This is the 11th byte from your solution.) This field is supposed to indicate the codec used but annoyingly there are a few entries used by multiple codecs. A full list of values is available from the MP4RA. From the list a few are relevant in this case.: 0x40 - MPEG-4 Audio 0x6B - MPEG-1 Audio (MPEG-1 Layers 1, 2, and 3) 0x69 - MPEG-2 Backward Compatible Audio (MPEG-2 Layers 1, 2, and 3) 0x67 - MPEG-2 AAC LC 0x6B and 0x69 denote MPEG-1 and 2 respectively layers 1, 2, and 3. 0x67 denotes MPEG-2 AAC LC but generally is unused in favor of 0x040 (0x66 and 0x68 are also MPEG-2 AAC profiles are seen even less frequently). 0x40 denotes MPEG-4 Audio. MPEG-4 Audio generally is thought of as AAC but there is a whole framework of audio codecs that can go in MPEG-4 Audio including AAC, BSAC, ALS, CELP, and something called MP3On4. MP3On4 is an MP3 variant with some new header information for multichannel. We can figure out what audio format is actually in the MPEG-4 Audio by looking at the the AudioSpecificConfig. This is the global header for the decoder that exists at byte 13 of the content of the 'esds' atom. At the begining of the AudioSpecificConfig there is a 5-bit AudioObjectType. A full list can be found on the multimedia wiki (that was linked in your post under the 'MPEG-4 Audio' article but here are the useful values: 00 - NULL 01 - AAC Main (a deprecated AAC profile from MPEG-2) 02 - AAC LC or backwards compatible HE-AAC (Most realworld AAC falls in one of these cases) 03 - AAC Scalable Sample Rate (rarely used) 03 - AAC LTP (a replacement for AAC Main, rarely used) 05 - HE-AAC explicitly signaled (Non-backward compatible) 22 - ER BSAC (A Korean broadcast codec) 23 - Low Delay AAC 29 - HE-AACv2 explicitly signaled (In one draft this was MP3On4 instead) 31 - ESCAPE (read 6 more bits, add 32) 32 - MP3on4 Layer 1 33 - MP3on4 Layer 2 34 - MP3on4 Layer 3 If you aren't worried about 'MP3On4' mp3 variant nor the other weird MPEG-4 Audio codecs then just use the objectTypeIndication. In the MPEG specifications these details are spread across 14496-1, -12, -14, and -3. Of these only 14496-12 is freely available.

参考：

mp4 atom - How to discriminate the audio codec? Is it AAC or MP3?

This section documents the ObjectTypeIndication used in MPEG-4 systems to indicate the type of streams. Applications for a new codec type will also automatically receive an object type indication. This table also occurs in ISO/IEC 14496-1 (various versions), the MPEG-4 systems specification. The intent is that the table maintained by this registration authority is the most up-to-date and definitive version. There is also an informative table of the current StreamType allocations.

Value	ObjectTypeIndication Description	Defined in/by
0x00	Forbidden
0x01	Systems ISO/IEC 14496-1 (a)	MPEG-4
0x02	Systems ISO/IEC 14496-1 (b)	MPEG-4
0x03	Interaction Stream	MPEG-4
0x04	Extended BIFS (h)	MPEG-4
0x05	AFX Stream (i)	MPEG-4
0x06	Font Data Stream	MPEG-4
0x07	Synthetised Texture	MPEG-4
0x08	Text Stream	MPEG-4
0x09	LASeR Stream	MPEG-4
0x0A	Simple Aggregation Format (SAF) Stream	MPEG-4
0x20	Visual ISO/IEC 14496-2 (c)	MPEG-4
0x21	Visual ITU-T Recommendation H.264 | ISO/IEC 14496-10 (g)	MPEG-4
0x22	Parameter Sets for ITU-T Recommendation H.264 | ISO/IEC 14496-10 (g)	MPEG-4
0x40	Audio ISO/IEC 14496-3 (d)	MPEG-4
0x60	Visual ISO/IEC 13818-2 Simple Profile	MPEG-4
0x61	Visual ISO/IEC 13818-2 Main Profile	MPEG-4
0x62	Visual ISO/IEC 13818-2 SNR Profile	MPEG-4
0x63	Visual ISO/IEC 13818-2 Spatial Profile	MPEG-4
0x64	Visual ISO/IEC 13818-2 High Profile	MPEG-4
0x65	Visual ISO/IEC 13818-2 422 Profile	MPEG-4
0x66	Audio ISO/IEC 13818-7 Main Profile	MPEG-4
0x67	Audio ISO/IEC 13818-7 LowComplexity Profile	MPEG-4
0x68	Audio ISO/IEC 13818-7 Scaleable Sampling Rate Profile	MPEG-4
0x69	Audio ISO/IEC 13818-3	MPEG-4
0x6A	Visual ISO/IEC 11172-2	MPEG-4
0x6B	Audio ISO/IEC 11172-3	MPEG-4
0x6C	Visual ISO/IEC 10918-1	MPEG-4
0x6D	Portable Network Graphics (f)	PNG
0x6E	Visual ISO/IEC 15444-1 (JPEG 2000)	MPEG-4
0xA0	EVRC Voice	3GPP2
0xA1	SMV Voice	3GPP2
0xA2	3GPP2 Compact Multimedia Format (CMF)	3GPP2
0xA3	SMPTE VC-1 Video	SMPTE
0xA4	Dirac Video Coder	Dirac
0xA5	AC-3 Audio	ETSI
0xA6	Enhanced AC-3 audio	ETSI
0xA7	DRA Audio	DRA
0xA8	ITU G.719 Audio	ITU G.719
0xA9	DTS Coherent Acoustics audio	DTS
0xAA	DTS-HD High Resolution Audio	DTS
0xAB	DTS-HD Master Audio	DTS
0xAC	DTS Express low bit rate audio, also known as DTS LBR	DTSE
0xC0 - 0xE0	user private
0xE1	13K Voice	3GPP2
0xE2 - 0xFE	user private
0xFF	no object type specified (e)	MPEG-4

1. This type is used for all 14496-1 streams unless specifically indicated to the contrary. Scene Description scenes, which are identified with StreamType=0x03 (see Table 9 ), using this object type value shall use the BIFSConfig specified in section 9.3.5.2.2  of this specification.
2. Used, with StreamType=0x03 (see Table 9 ), for Scene Description streams that use the BIFSv2Config. Its use with other StreamTypes is reserved .
3. Includes associated Amendment(s) and Corrigendum(a). The actual object types are defined in ISO/IEC 14496-2 and are conveyed in the DecoderSpecificInfo as specified in ISO/IEC 14496-2, Annex K.
4. Includes associated Amendment(s) and Corrigendum(a). The actual object types are defined in ISO/IEC 14496-3 and are conveyed in the DecoderSpecificInfo as specified in ISO/IEC 14496-3 subpart 1 subclause 6.2.1.
5. Streams with this value with a StreamType indicating a systems stream (values 1,2,3, 6, 7, 8, 9) shall be treated as if the ObjectTypeIndication had been set to 0x01.
6. For PNG Streams, the following configuration/rules apply:
   • StreamType: 0x04 (visual)
   • No decoder specific info needed
   • The PNG stream shall consist in only one (1) AccessUnit
   • The PNG stream access unit shall contain the complete PNG image/file
   • MNG shall not be used inside PNG streams
7. Includes associated Amendment(s) and Corrigendum(a). The actual object types are defined in ITU-T Recommendation H.264 | ISO/IEC 14496-10 and are conveyed in the DecoderSpecificInfo.
8. Used,  with StreamType=0x03, for Scene Description streams that use the BIFSConfigEx; its use with other StreamTypes is reserved. (Was previously reserved for MUCommandStream but not used for that purpose.)
9. Used,  with StreamType=0x03, for Scene Description streams that use the AFXConfig; its use with other StreamTypes is reserved.

Value	StreamType Description
0x00	Forbidden
0x01	ObjectDescriptorStream (see 8.5)
0x02	ClockReferenceStream (see 10.2.5)
0x03	SceneDescriptionStream (see 9.2.1)
0x04	VisualStream
0x05	AudioStream
0x06	MPEG7Stream
0x07	IPMPStream (see 8.3.2)
0x08	ObjectContentInfoStream (see 8.4.2)
0x09	MPEGJStream
0x0A	Interaction Stream
0x0B	IPMPToolStream
0x0C	FontDataStream
0x0D	StreamingText
0x20- 0x3F	user private

参考：http://www.mp4ra.org/object.html