MPEG-4 Audio 关于esds 记录

分手后的思念是犯贱 2022-05-22 07:57 224阅读 0赞

[https://blog.csdn.net/djhsws/article/details/53522060][https_blog.csdn.net_djhsws_article_details_53522060]

# MPEG-4 Audio 关于esds 记录 #

2016年12月08日 17:51:48

阅读数：1564

当解析Mp4的时候，会碰到这个esds 的box，这个box 有很多信息。  
当时是为了解决在MP4A中如何判断是acc还是 MP3  
然后找到下面答案  
[https://wiki.multimedia.cx/index.php?title=MPEG-4\_Audio][https_wiki.multimedia.cx_index.php_title_MPEG-4_Audio]  
[http://stackoverflow.com/questions/3987850/mp4-atom-how-to-discriminate-the-audio-codec-is-it-aac-or-mp3][http_stackoverflow.com_questions_3987850_mp4-atom-how-to-discriminate-the-audio-codec-is-it-aac-or-mp3]  
现在梳理下

在Audio Trak 的esds box中

首先是  
1、version 和 flag 占4个字节 不使用就跳过

get_be32(m_it); /* version + flags */

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2、MP4ESDescrTag 读取 MP4ESDescrTag tag 和 len 和附属内容

tag = get_byte(m_it);
            len = getTaglen();
            if (tag == MP4ESDescrTag) {
                get_be16(m_it); /* ID */
                get_byte(m_it); /* priority */
            } else
                get_be16(m_it); /* ID */

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3、MP4DecConfigDescrTag 读取 MP4DecConfigDescrTag tag 和 len 和附属内容

tag = get_byte(m_it);
    len = getTaglen();
            if (tag == MP4DecConfigDescrTag) {
                int object_type_id = get_byte(m_it);
                get_byte(m_it); /* stream type */
                get_byte(m_it); get_byte(m_it); get_byte(m_it); 
                get_be32(m_it); /* max bitrate */
                get_be32(m_it); /* avg bitrate */
                st->codec->codec_id= codec_get_id(ff_mp4_obj_type, object_type_id);

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这边的附属内容我要说下 重要的是 这边对codec 解码进行了调整，id 对应表**附件1**，这边决定了MP3 或者 acc等

4、 MP4DecSpecificDescrTag 读取MP4DecSpecificDescrTag 和len 和附属内容

tag = get_byte(m_it);
    len=getTagLen();
    if (tag == MP4DecSpecificDescrTag) {
        st->codec->extradata = (uint8_t *)malloc(len);
        if (st->codec->extradata) {
        ReadData(st->codec->extradata, len,m_it);
        st->codec->extradata_size = len;
        int ad = *st->codec->extradata;
        int aa =*st->codec->extradata >> 3;
        if ((*st->codec->extradata >> 3) == 29) {
            st->codec->codec_id = CODEC_ID_MP3ON4;
        }
        if (st->codec->codec_id == CODEC_ID_AAC) {
            MPEG4AudioConfig cfg = {
         0};
            avpriv_mpeg4audio_get_config(&cfg, st->codec->extradata,
                                st->codec->extradata_size, 1);
            st->codec->channels = cfg.channels;
    
    //  if (cfg.object_type == 29 && cfg.sampling_index < 3) // old mp3on4
    //st->codec->sample_rate = avpriv_mpa_freq_tab[cfg.sampling_index];
    //  else if (cfg.ext_sample_rate)
    //  //st->codec->sample_rate = cfg.ext_sample_rate;
    //  else
    //  //st->codec->sample_rate = cfg.sample_rate;         
    //  if (!(st->codec->codec_id = ff_codec_get_id(mp4_audio_types,
    //      cfg.object_type)))
    //  st->codec->codec_id = AV_CODEC_ID_AAC;
      }
    }

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这边就严重了，这边如果是老的版本 只需如此

int aa =*st->codec->extradata >> 3;
    if ((*st->codec->extradata >> 3) == 29) {
        st->codec->codec_id = CODEC_ID_MP3ON4;
    }

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但是新的 版本 调整增加了 很多内容

The Audio Specific Config is the global header for MPEG-4 Audio:
    5 bits: object type
    if (object type == 31)
        6 bits + 32: object type
    4 bits: frequency index
    if (frequency index == 15)
        24 bits: frequency
    4 bits: channel configuration
    var bits: AOT Specific Config

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*  主要如上 object type 读取5个bit object type列表见附件2（对codec解码器进行调整，MP3 还是ACC还是 MP3on4）
 *  然后 frequency index 读取4个bit frequency index 列表见 附件3（对采样率进行调整）
 *  最后channel 读取4个位 列表见附件4 （对声道数进行调整）

附件1  
const MP4CodecTag ff\_mp4\_obj\_type\[\] = \{  
\{ CODEC\_ID\_MPEG4 , 32 \},  
\{ CODEC\_ID\_H264 , 33 \},  
\{ CODEC\_ID\_AAC , 64 \},  
\{ CODEC\_ID\_MPEG2VIDEO, 96 \}, /\* MPEG2 Simple \*/  
\{ CODEC\_ID\_MPEG2VIDEO, 97 \}, /\* MPEG2 Main \*/  
\{ CODEC\_ID\_MPEG2VIDEO, 98 \}, /\* MPEG2 SNR \*/  
\{ CODEC\_ID\_MPEG2VIDEO, 99 \}, /\* MPEG2 Spatial \*/  
\{ CODEC\_ID\_MPEG2VIDEO, 100 \}, /\* MPEG2 High \*/  
\{ CODEC\_ID\_MPEG2VIDEO, 101 \}, /\* MPEG2 422 \*/  
\{ CODEC\_ID\_AAC , 102 \}, /\* MPEG2 AAC Main \*/  
\{ CODEC\_ID\_AAC , 103 \}, /\* MPEG2 AAC Low \*/  
\{ CODEC\_ID\_AAC , 104 \}, /\* MPEG2 AAC SSR \*/  
\{ CODEC\_ID\_MP3 , 105 \}, /\* 13818-3 \*/  
\{ CODEC\_ID\_MPEG1VIDEO, 106 \}, /\* 11172-2 \*/  
\{ CODEC\_ID\_MP3 , 107 \}, /\* 11172-3 \*/  
\{ CODEC\_ID\_MJPEG , 108 \}, /\* 10918-1 \*/  
\{ CODEC\_ID\_PNG , 109 \},  
\{ CODEC\_ID\_JPEG2000 , 110 \}, /\* 15444-1 \*/  
\{ CODEC\_ID\_VC1 , 163 \},  
\{ CODEC\_ID\_VORBIS , 221 \},  
\{ CODEC\_ID\_PCM\_S16LE , 224 \},  
\{ CODEC\_ID\_QCELP , 225 \},  
\{ CODEC\_ID\_AC3 , 226 \},  
\{ CODEC\_ID\_PCM\_ALAW , 227 \},  
\{ CODEC\_ID\_PCM\_MULAW , 228 \},  
\{ CODEC\_ID\_PCM\_S16BE , 230 \},  
\{ CODEC\_ID\_H263 , 242 \},  
\{ CODEC\_ID\_H261 , 243 \},  
\{ CODEC\_ID\_NONE, 0 \},

};

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附件2  
MPEG-4 Audio Object Types:  
● 0: Null  
● 1: AAC Main  
● 2: AAC LC (Low Complexity)  
● 3: AAC SSR (Scalable Sample Rate)  
● 4: AAC LTP (Long Term Prediction)  
● 5: SBR (Spectral Band Replication)  
● 6: AAC Scalable  
● 7: TwinVQ  
● 8: CELP (Code Excited Linear Prediction)  
● 9: HXVC (Harmonic Vector eXcitation Coding)  
● 10: Reserved  
● 11: Reserved  
● 12: TTSI (Text-To-Speech Interface)  
● 13: Main Synthesis  
● 14: Wavetable Synthesis  
● 15: General MIDI  
● 16: Algorithmic Synthesis and Audio Effects  
● 17: ER (Error Resilient) AAC LC  
● 18: Reserved  
● 19: ER AAC LTP  
● 20: ER AAC Scalable  
● 21: ER TwinVQ  
● 22: ER BSAC (Bit-Sliced Arithmetic Coding)  
● 23: ER AAC LD (Low Delay)  
● 24: ER CELP  
● 25: ER HVXC  
● 26: ER HILN (Harmonic and Individual Lines plus Noise)  
● 27: ER Parametric  
● 28: SSC (SinuSoidal Coding)  
● 29: PS (Parametric Stereo)  
● 30: MPEG Surround  
● 31: (Escape value)  
● 32: Layer-1  
● 33: Layer-2  
● 34: Layer-3  
● 35: DST (Direct Stream Transfer)  
● 36: ALS (Audio Lossless)  
● 37: SLS (Scalable LosslesS)  
● 38: SLS non-core  
● 39: ER AAC ELD (Enhanced Low Delay)  
● 40: SMR (Symbolic Music Representation) Simple  
● 41: SMR Main  
● 42: USAC (Unified Speech and Audio Coding) (no SBR)  
● 43: SAOC (Spatial Audio Object Coding)  
● 44: LD MPEG Surround  
● 45: USAC  
附件3  
Sampling Frequencies  
There are 13 supported frequencies:  
● 0: 96000 Hz  
● 1: 88200 Hz  
● 2: 64000 Hz  
● 3: 48000 Hz  
● 4: 44100 Hz  
● 5: 32000 Hz  
● 6: 24000 Hz  
● 7: 22050 Hz  
● 8: 16000 Hz  
● 9: 12000 Hz  
● 10: 11025 Hz  
● 11: 8000 Hz  
● 12: 7350 Hz  
● 13: Reserved  
● 14: Reserved  
● 15: frequency is written explictly  
附件3

Channel Configurations  
These are the channel configurations:  
● 0: Defined in AOT Specifc Config  
● 1: 1 channel: front-center  
● 2: 2 channels: front-left, front-right  
● 3: 3 channels: front-center, front-left, front-right  
● 4: 4 channels: front-center, front-left, front-right, back-center  
● 5: 5 channels: front-center, front-left, front-right, back-left, back-right  
● 6: 6 channels: front-center, front-left, front-right, back-left, back-right, LFE-channel  
● 7: 8 channels: front-center, front-left, front-right, side-left, side-right, back-left, back-right, LFE-channel  
● 8-15: Reserved

[https_blog.csdn.net_djhsws_article_details_53522060]: https://blog.csdn.net/djhsws/article/details/53522060
[https_wiki.multimedia.cx_index.php_title_MPEG-4_Audio]: https://wiki.multimedia.cx/index.php?title=MPEG-4_Audio
[http_stackoverflow.com_questions_3987850_mp4-atom-how-to-discriminate-the-audio-codec-is-it-aac-or-mp3]: http://stackoverflow.com/questions/3987850/mp4-atom-how-to-discriminate-the-audio-codec-is-it-aac-or-mp3