分段录制的实现

分段录制也就是可以暂停之后恢复录制，并且录制结束之后是在同一个文件中。不管video还是audio都是有时间戳的frame，真是因为有时间戳播放器才能有序的进行播放了。因此在分段录制中，只要在暂停的时候记录一下当前的一个时间戳，然后在恢复之后计算一下这之间的时间差，然后在将这个frame写入之前修改一下这个frame的时间戳就行了。原理还是蛮简单的，因此实现也简单的多了。code说明一切，需要的咨询读一下代码。

- (void)captureOutput:(AVCaptureOutput *)captureOutput didOutputSampleBuffer:(CMSampleBufferRef)sampleBuffer fromConnection:(AVCaptureConnection *)connection{        @synchronized(self)    {        if(!self.isRecording||self.isPause){            return;        }                BOOL isVideo = YES;        if(captureOutput == self.audioOutput){            isVideo = NO;        }                if(![self processSampleBuffer:sampleBuffer isVideo:isVideo]){                        if((sampleBuffer = [self processPartialRecord:sampleBuffer isVideo:isVideo]))            {                [self encodeFrame:sampleBuffer isVideo:isVideo];                CFRelease(sampleBuffer);            }                    }            }    }- (CMSampleBufferRef)processPartialRecord:(CMSampleBufferRef)sampleBuffer isVideo:(BOOL)isVideo{    if (_interrupted){        if (isVideo){            return nil;        }        _interrupted = NO;                CMTime presentTimeStamp = CMSampleBufferGetPresentationTimeStamp(sampleBuffer);        CMTime last = isVideo ? _lastVideo : _lastAudio;        if (CMTIME_IS_VALID(last)){            if (CMTIME_IS_VALID(_timeOffset)){                presentTimeStamp = CMTimeSubtract(presentTimeStamp, _timeOffset);            }            CMTime offset = CMTimeSubtract(presentTimeStamp, last);            [self logCMTime:offset];            if (_timeOffset.value == 0){                _timeOffset = offset;            }            else{                _timeOffset = CMTimeAdd(_timeOffset, offset);            }        }        _lastVideo.flags = 0;        _lastAudio.flags = 0;    }        CFRetain(sampleBuffer);    if (_timeOffset.value > 0){        CFRelease(sampleBuffer);        sampleBuffer = [self adjustTime:sampleBuffer by:_timeOffset];    }        CMTime presentTimeStamp = CMSampleBufferGetPresentationTimeStamp(sampleBuffer);    CMTime duration = CMSampleBufferGetDuration(sampleBuffer);    if (duration.value > 0){        presentTimeStamp = CMTimeAdd(presentTimeStamp, duration);    }        if (isVideo){        _lastVideo = presentTimeStamp;    }    else{        _lastAudio = presentTimeStamp;    }        return sampleBuffer;}- (CMSampleBufferRef) adjustTime:(CMSampleBufferRef) sample by:(CMTime) offset{    CMItemCount count;    CMSampleBufferGetSampleTimingInfoArray(sample, 0, nil, &count);    CMSampleTimingInfo* pInfo = malloc(sizeof(CMSampleTimingInfo) * count);    CMSampleBufferGetSampleTimingInfoArray(sample, count, pInfo, &count);        for (CMItemCount i = 0; i < count; i++){        pInfo[i].decodeTimeStamp = CMTimeSubtract(pInfo[i].decodeTimeStamp, offset);        pInfo[i].presentationTimeStamp = CMTimeSubtract(pInfo[i].presentationTimeStamp, offset);    }        CMSampleBufferRef sout;    CMSampleBufferCreateCopyWithNewTiming(nil, sample, count, pInfo, &sout);    free(pInfo);    return sout;}- (BOOL) encodeFrame:(CMSampleBufferRef) sampleBuffer isVideo:(BOOL)isVideo{    if (CMSampleBufferDataIsReady(sampleBuffer))    {        if (_writer.status == AVAssetWriterStatusUnknown){            CMTime startTime = CMSampleBufferGetPresentationTimeStamp(sampleBuffer);            [_writer startWriting];            [_writer startSessionAtSourceTime:startTime];        }        if (_writer.status == AVAssetWriterStatusFailed){            NSLog(@"error %@", _writer.error.localizedDescription);            return NO;        }                if (isVideo){            if (self.videoWriterInput.readyForMoreMediaData){                [self.videoWriterInput appendSampleBuffer:sampleBuffer];                return YES;            }        }else{            if(self.audioWriterInput.readyForMoreMediaData){                [self.audioWriterInput appendSampleBuffer:sampleBuffer];                return YES;            }        }    }    return NO;}