Open Radar

 
We are seeing that H264 consistently outperforms HEVC in terms of SSIM at 3 Mbps with a 1280x720 resolution. Please find attached the SSIM and PSNR of encoding the same asset on an iPhone 8 running iOS 12.1 at various bitrates using both HEVC and H264, as well as driver code. SSIM and PSNR were measured with FFmpeg using the following command: ffmpeg -i hevc.mp4 -i video.mp4 -lavfi "ssim;[0:v][1:v]psnr" -f null -

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+------+----------+----------+--+------+-----------+-----------+
| SSIM |          |          |  | PSNR |           |           |
+------+----------+----------+--+------+-----------+-----------+
| Mbps | H264     | HEVC     |  | Mbps | H264      | HEVC      |
| 1.6  | 0.868546 | 0.866705 |  | 1.6  | 28.742276 | 29.012076 |
| 1.8  | 0.878769 | 0.870306 |  | 1.8  | 29.127728 | 29.145616 |
| 2.0  | 0.887289 | 0.876988 |  | 2.0  | 29.493496 | 29.401263 |
| 2.2  | 0.894511 | 0.885587 |  | 2.2  | 29.826788 | 29.753897 |
| 2.4  | 0.901402 | 0.892895 |  | 2.4  | 30.168525 | 30.083894 |
| 2.6  | 0.907192 | 0.901793 |  | 2.6  | 30.482898 | 30.523067 |
| 2.8  | 0.912267 | 0.910082 |  | 2.8  | 30.776906 | 30.990894 |
| 3.0  | 0.916828 | 0.916097 |  | 3.0  | 31.044133 | 31.348581 |
| 3.2  | 0.921024 | 0.921129 |  | 3.2  | 31.316162 | 31.696412 |
| 3.4  | 0.924703 | 0.926292 |  | 3.4  | 31.564169 | 32.059309 |
| 3.6  | 0.928121 | 0.930604 |  | 3.6  | 31.793409 | 32.375958 |
| 3.8  | 0.931357 | 0.933995 |  | 3.8  | 32.039006 | 32.647455 |
| 4.2  | 0.936885 | 0.940416 |  | 4.2  | 32.458297 | 33.190408 |
| 4.7  | 0.942769 | 0.946592 |  | 4.7  | 32.956044 | 33.77437  |
| 5.6  | 0.951091 | 0.955087 |  | 5.6  | 33.749049 | 34.707639 |
| 7.2  | 0.961685 | 0.964716 |  | 7.2  | 34.977282 | 35.99391  |
| 10.8 | 0.974855 | 0.97714  |  | 10.8 | 37.143887 | 38.316594 |
| 14.4 | 0.98164  | 0.983663 |  | 14.4 | 38.844081 | 40.099846 |
| 21.6 | 0.988423 | 0.989922 |  | 21.6 | 41.34255  | 42.658182 |
| 28.8 | 0.991736 | 0.992605 |  | 28.8 | 43.166993 | 44.312512 |
| 43.2 | 0.995039 | 0.994992 |  | 43.2 | 45.774187 | 46.329256 |
| 57.6 | 0.996671 | 0.995594 |  | 57.6 | 47.556865 | 47.045504 |
+------+----------+----------+--+------+-----------+-----------+

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- (void)testCodec:(AVVideoCodecType)codec withBitrate:(CGFloat)bitRate {
    NSURL *const outputUrl = [[[NSURL fileURLWithPath:NSTemporaryDirectory()]
                               URLByAppendingPathComponent:[[NSUUID UUID] UUIDString]]
                              URLByAppendingPathExtension:@"mp4"];

    NSURL *const url = [[NSBundle bundleForClass:[self class]] URLForResource:@"video" withExtension:@"mp4"];
    AVAsset *const asset = [AVAsset assetWithURL:url];
    AVAssetTrack *const videoTrack = [[asset tracksWithMediaType:AVMediaTypeVideo] firstObject];
    NSError *error = nil;
    AVAssetReader *const assetReader = [AVAssetReader assetReaderWithAsset:asset error:&error];
    XCTAssertNil(error);
    AVAssetWriter *const assetWriter = [AVAssetWriter assetWriterWithURL:outputUrl fileType:AVFileTypeMPEG4 error:&error];
    XCTAssertNil(error);

    AVAssetWriterInput *const input = [[AVAssetWriterInput alloc] initWithMediaType:AVMediaTypeVideo
                                                                     outputSettings:@{
                                                                                      AVVideoCodecKey: codec,
                                                                                      AVVideoWidthKey: @(1280),
                                                                                      AVVideoHeightKey: @(720),
                                                                                      AVVideoCompressionPropertiesKey: @{
                                                                                              AVVideoAverageBitRateKey: @(bitRate),
                                                                                              }
                                                                                      }];

    AVAssetReaderOutput *const output = [[AVAssetReaderTrackOutput alloc] initWithTrack:videoTrack
                                                                         outputSettings:@{
                                                                                          (id)kCVPixelBufferPixelFormatTypeKey:
                                                                                              @(kCVPixelFormatType_32BGRA),
                                                                                          }];

    [assetReader addOutput:output];
    [assetWriter addInput:input];

    XCTAssertNil(assetReader.error);
    XCTAssertNil(assetWriter.error);

    [assetReader startReading];
    [assetWriter startWriting];

    [assetWriter startSessionAtSourceTime:kCMTimeZero];

    const dispatch_queue_t queue = dispatch_queue_create("transcode", DISPATCH_QUEUE_SERIAL);
    const dispatch_semaphore_t transcode = dispatch_semaphore_create(0);
    [input requestMediaDataWhenReadyOnQueue:queue usingBlock:^{
        while ([input isReadyForMoreMediaData]) {
            const CMSampleBufferRef sampleBuffer = [output copyNextSampleBuffer];

            XCTAssertNil(assetReader.error);
            XCTAssertNil(assetWriter.error);

            if (sampleBuffer) {
                [input appendSampleBuffer:sampleBuffer];
                CFRelease(sampleBuffer);
            } else {
                [input markAsFinished];
                dispatch_semaphore_signal(transcode);
            }
        }
    }];

    dispatch_semaphore_wait(transcode, DISPATCH_TIME_FOREVER);

    const dispatch_semaphore_t write = dispatch_semaphore_create(0);
    [assetWriter finishWritingWithCompletionHandler:^{
        dispatch_semaphore_signal(write);
    }];

    XCTAssertNil(assetWriter.error);

    dispatch_semaphore_wait(write, DISPATCH_TIME_FOREVER);

    NSLog(@"Wrote to %@", outputUrl);
}

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