去年因为视频压缩转码方面的一些需求需要判断 AVAsset 的编码类型是否为 H.264，然后就整理了这篇笔记，但是忘记发出来了
思路大概分三步：
1.从 AVAsset 的轨道中取出视频轨道
2.从视频轨道中获取视频格式信息
3.从视频格式信息中获取视频编码类型
AVAsset 的轨道集合：
/*!
@property tracks
@abstract Provides the array of AVAssetTracks contained by the asset
*/
@property (nonatomic, readonly) NSArray *tracks;
以下代码可以建一个 AVAsset 的 Category
@implementation AVAsset (PSExtends)
/// 1.从 AVAsset 的轨道中取出视频轨道
- (AVAssetTrack *)ps_videoAssetTrack
{
NSArray *tracksArray = self.tracks;
AVAssetTrack *videoAssetTrack = nil;
for (AVAssetTrack *track in tracksArray) {
if ([track.mediaType isEqualToString:AVMediaTypeVideo]) {
videoAssetTrack = track;
break;
}
}
return videoAssetTrack;
}
- (BOOL)ps_isH264
{
BOOL isH264 = NO;
AVAssetTrack *videoAssetTrack = [self ps_videoAssetTrack];
if (videoAssetTrack) {
isH264 = videoAssetTrack.ps_isH264;
}
return isH264;
}
- (BOOL)ps_isHEVC
{
BOOL isHEVC = NO;
AVAssetTrack *videoAssetTrack = [self ps_videoAssetTrack];
if (videoAssetTrack) {
isHEVC = videoAssetTrack.ps_isHEVC;
}
return isHEVC;
}
@end
@implementation AVAssetTrack (PSExtends)
/// 2.从视频轨道中获取视频格式信息
- (CMFormatDescriptionRef)ps_CMFormatDescriptionRef
{
NSArray *formatDescriptions = [self formatDescriptions];
CMFormatDescriptionRef formatDescription = (__bridge CMFormatDescriptionRef)(formatDescriptions.firstObject);
return formatDescription;
}
/// 3.从视频格式信息中获取视频编码类型
- (CMVideoCodecType)ps_CMVideoCodecType
{
CMFormatDescriptionRef formatDescription = [self ps_CMFormatDescriptionRef];
CMVideoCodecType codecType = CMVideoFormatDescriptionGetCodecType(formatDescription);
return codecType;
}
- (BOOL)ps_isH264
{
BOOL isH264 = NO;
CMVideoCodecType codecType = [self ps_CMVideoCodecType];
isH264 = (codecType == kCMVideoCodecType_H264);
return isH264;
}
- (BOOL)ps_isHEVC
{
BOOL isHEVC = NO;
CMVideoCodecType codecType = [self ps_CMVideoCodecType];
isHEVC = (codecType == kCMVideoCodecType_HEVC);
return isHEVC;
}
@end
其他编码类型：
/*!
@enum CMVideoCodecType
@discussion Four-character codes identifying the video codec. Certain codec types are also pixel formats.
Note: There is no kCMVideoCodecType_Raw -- use the appropriate pixel format type as the codec type.
@constant kCMVideoCodecType_422YpCbCr8 Component Y'CbCr 8-bit 4:2:2 ordered Cb Y'0 Cr Y'1
@constant kCMVideoCodecType_Animation Apple Animation format
@constant kCMVideoCodecType_Cinepak Cinepak format
@constant kCMVideoCodecType_JPEG Joint Photographic Experts Group (JPEG) format
@constant kCMVideoCodecType_JPEG_OpenDML JPEG format with Open-DML extensions
@constant kCMVideoCodecType_SorensonVideo Sorenson video format
@constant kCMVideoCodecType_SorensonVideo3 Sorenson 3 video format
@constant kCMVideoCodecType_H263 ITU-T H.263 format
@constant kCMVideoCodecType_H264 ITU-T H.264 format (AKA ISO/IEC 14496-10 - MPEG-4 Part 10, Advanced Video Coding format)
@constant kCMVideoCodecType_HEVC ITU-T HEVC format
@constant kCMVideoCodecType_HEVCWithAlpha HEVC format with alpha support defined in Annex-F.
IMPORTANT NOTE: this constant is used to select the appropriate encoder, but is NOT used on the encoded content,
which is backwards compatible and hence uses 'hvc1' as its codec type.
@constant kCMVideoCodecType_MPEG4Video ISO/IEC Moving Picture Experts Group (MPEG) MPEG-4 Part 2 video format
@constant kCMVideoCodecType_MPEG2Video MPEG-2 video format
@constant kCMVideoCodecType_MPEG1Video MPEG-1 video format
@constant kCMVideoCodecType_DVCNTSC DV NTSC format
@constant kCMVideoCodecType_DVCPAL DV PAL format
@constant kCMVideoCodecType_DVCProPAL Panasonic DVCPro PAL format
@constant kCMVideoCodecType_DVCPro50NTSC Panasonic DVCPro-50 NTSC format
@constant kCMVideoCodecType_DVCPro50PAL Panasonic DVCPro-50 PAL format
@constant kCMVideoCodecType_DVCPROHD720p60 Panasonic DVCPro-HD 720p60 format
@constant kCMVideoCodecType_DVCPROHD720p50 Panasonic DVCPro-HD 720p50 format
@constant kCMVideoCodecType_DVCPROHD1080i60 Panasonic DVCPro-HD 1080i60 format
@constant kCMVideoCodecType_DVCPROHD1080i50 Panasonic DVCPro-HD 1080i50 format
@constant kCMVideoCodecType_DVCPROHD1080p30 Panasonic DVCPro-HD 1080p30 format
@constant kCMVideoCodecType_DVCPROHD1080p25 Panasonic DVCPro-HD 1080p25 format
@constant kCMVideoCodecType_AppleProRes4444XQ Apple ProRes 4444 XQ format
@constant kCMVideoCodecType_AppleProRes4444 Apple ProRes 4444 format
@constant kCMVideoCodecType_AppleProRes422HQ Apple ProRes 422 HQ format
@constant kCMVideoCodecType_AppleProRes422 Apple ProRes 422 format
@constant kCMVideoCodecType_AppleProRes422LT Apple ProRes 422 LT format
@constant kCMVideoCodecType_AppleProRes422Proxy Apple ProRes 422 Proxy format
@constant kCMVideoCodecType_AppleProResRAW Apple ProRes RAW format
@constant kCMVideoCodecType_AppleProResRAWHQ Apple ProRes RAW HQ format
*/
typedef FourCharCode CMVideoCodecType API_AVAILABLE(macos(10.7), ios(4.0), tvos(9.0), watchos(6.0));
#if COREMEDIA_USE_DERIVED_ENUMS_FOR_CONSTANTS
enum : CMVideoCodecType
#else
enum
#endif
{
kCMVideoCodecType_422YpCbCr8 = kCMPixelFormat_422YpCbCr8,
kCMVideoCodecType_Animation = 'rle ',
kCMVideoCodecType_Cinepak = 'cvid',
kCMVideoCodecType_JPEG = 'jpeg',
kCMVideoCodecType_JPEG_OpenDML = 'dmb1',
kCMVideoCodecType_SorensonVideo = 'SVQ1',
kCMVideoCodecType_SorensonVideo3 = 'SVQ3',
kCMVideoCodecType_H263 = 'h263',
kCMVideoCodecType_H264 = 'avc1',
kCMVideoCodecType_HEVC = 'hvc1',
kCMVideoCodecType_HEVCWithAlpha = 'muxa',
kCMVideoCodecType_MPEG4Video = 'mp4v',
kCMVideoCodecType_MPEG2Video = 'mp2v',
kCMVideoCodecType_MPEG1Video = 'mp1v',
kCMVideoCodecType_VP9 = 'vp09',
kCMVideoCodecType_DVCNTSC = 'dvc ',
kCMVideoCodecType_DVCPAL = 'dvcp',
kCMVideoCodecType_DVCProPAL = 'dvpp',
kCMVideoCodecType_DVCPro50NTSC = 'dv5n',
kCMVideoCodecType_DVCPro50PAL = 'dv5p',
kCMVideoCodecType_DVCPROHD720p60 = 'dvhp',
kCMVideoCodecType_DVCPROHD720p50 = 'dvhq',
kCMVideoCodecType_DVCPROHD1080i60 = 'dvh6',
kCMVideoCodecType_DVCPROHD1080i50 = 'dvh5',
kCMVideoCodecType_DVCPROHD1080p30 = 'dvh3',
kCMVideoCodecType_DVCPROHD1080p25 = 'dvh2',
kCMVideoCodecType_AppleProRes4444XQ = 'ap4x',
kCMVideoCodecType_AppleProRes4444 = 'ap4h',
kCMVideoCodecType_AppleProRes422HQ = 'apch',
kCMVideoCodecType_AppleProRes422 = 'apcn',
kCMVideoCodecType_AppleProRes422LT = 'apcs',
kCMVideoCodecType_AppleProRes422Proxy = 'apco',
kCMVideoCodecType_AppleProResRAW = 'aprn',
kCMVideoCodecType_AppleProResRAWHQ = 'aprh',
} API_AVAILABLE(macos(10.7), ios(4.0), tvos(9.0), watchos(6.0));