Flv视频格式解析
Flv文件分为2部分，头和数据部分。
Flv视频头
标准的视频头如下：
| Field | Data Type | Default | Details |
|---|---|---|---|
| Signature | byte[3] | “FLV” | Always “FLV” |
| Version | uint8 | 1 | Only 0x01 is valid |
| Flags | uint8 bitmask | 0x05 | Bitmask: 0x04 is audio, 0x01 is video (so 0x05 is audio+video) |
| Header Size | uint32_be | 9 | Used to skip a newer expanded header |
数据
视频头结束后，是数据部分，这部分是由一个一个的FLV tags组成，这个tag中包含一个15字节的头，其后紧跟实际的数据。头的前4个自己用来说明前面的 FLV tags的大小，主要用来回放（向前拖动）
| Field | Data Type | Default | Details |
|---|---|---|---|
| Size of previous packet | uint32_be | 0 | For first packet set to NULL |
| Packet Type | uint8 | 18 | For first packet set to AMF Metadata |
| Payload Size | uint24_be | varies | Size of packet data only |
| Timestamp Lower | uint24_be | 0 | For first packet set to NULL |
| Timestamp Upper | uint8 | 0 | Extension to create a uint32_be value |
| Stream ID | uint24_be | 0 | For first stream of same type set to NULL |
| Payload Data | freeform | varies | Data as defined by packet type |
支持的视频编码：
| Id | Video encoding |
|---|---|
| 0 | RGB |
| 1 | run-length |
| 2 | Sorenson's H.263 |
| 3 | Screen 1 |
| 4 | On2 TrueMotion VP6 |
| 5 | VP6 with alpha |
| 6 | Screen 2 |
| 7 | MP4 H.264 |
| 8 | ITU H.263 |
| 9 | MPEG-4 ASP. |
支持的音频编码：
| Id | Audio encoding |
|---|---|
| 0 | native PCM |
| 1 | ADPCM |
| 2 | MPEG layer 3 |
| 3 | PCM – little endian |
| 4 | Asao 16 kHz |
| 5 | Asao 8 kHz |
| 6 | Asao parameter rate |
| 7 | a-law |
| 8 | μ-law |
| Id | Audio encoding |
|---|---|
| 10 | MP4 AAC |
| 11 | Speex |
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