I'm doing random access sampling from AVAsset of local h264 video file
let track = asset.tracks(withMediaType: .video)[0]
let assetReader = try! AVAssetReader(asset: asset)
let trackOutput = AVAssetReaderTrackOutput(track: track, outputSettings: nil)
trackOutput.supportsRandomAccess = true
assetReader.add(trackOutput)
assetReader.startReading()
...
let targetFrameDTS = CMTime(value: 56, timescale: 30)
let timeRange = CMTimeRange(
start: CMTimeAdd(time, CMTime(value: -1, timescale: 30)),
duration: CMTime(value: 2, timescale: 30)
)
// reset output to be near target frame decoding time
trackOutput.reset(forReadingTimeRanges: [NSValue(timeRange: timeRange)])
while assetReader.status == .reading {
guard let sample = trackOutput.copyNextSampleBuffer() else { break }
let dts = CMSampleBufferGetDecodeTimeStamp(sample)
print("\(dts.value)/\(dts.timescale)")
}
for some reason with some targetFrameDTS assetReader copyNextSampleBuffer will skip samples. in my particular case the output is
...
47/30
48/30
50/30
51/30
54/30
55/30
57/30
why is it so?
