How to use AVSampleBufferDisplayLayer in iOS 8 for RTP H264 Streams with GStreamer?

Question

After getting notice of the HW-H264-Decoder being available to programmers in iOS 8, I want to use it now. There is a nice introduction to 'Direct Access to Video Encoding and Decoding' from WWDC 2014 out there. You can take a look here.

Based on Case 1 there, I started to develop an Application, that should be able to get an H264-RTP-UDP-Stream from GStreamer, sink it into an 'appsink'-element to get direct access to the NAL Units and do the conversion to create CMSampleBuffers, which my AVSampleBufferDisplayLayer can display then.

The interesting piece of code doing all that is the following:

//
//  GStreamerBackend.m
// 

#import "GStreamerBackend.h"

NSString * const naluTypesStrings[] = {
    @"Unspecified (non-VCL)",
    @"Coded slice of a non-IDR picture (VCL)",
    @"Coded slice data partition A (VCL)",
    @"Coded slice data partition B (VCL)",
    @"Coded slice data partition C (VCL)",
    @"Coded slice of an IDR picture (VCL)",
    @"Supplemental enhancement information (SEI) (non-VCL)",
    @"Sequence parameter set (non-VCL)",
    @"Picture parameter set (non-VCL)",
    @"Access unit delimiter (non-VCL)",
    @"End of sequence (non-VCL)",
    @"End of stream (non-VCL)",
    @"Filler data (non-VCL)",
    @"Sequence parameter set extension (non-VCL)",
    @"Prefix NAL unit (non-VCL)",
    @"Subset sequence parameter set (non-VCL)",
    @"Reserved (non-VCL)",
    @"Reserved (non-VCL)",
    @"Reserved (non-VCL)",
    @"Coded slice of an auxiliary coded picture without partitioning (non-VCL)",
    @"Coded slice extension (non-VCL)",
    @"Coded slice extension for depth view components (non-VCL)",
    @"Reserved (non-VCL)",
    @"Reserved (non-VCL)",
    @"Unspecified (non-VCL)",
    @"Unspecified (non-VCL)",
    @"Unspecified (non-VCL)",
    @"Unspecified (non-VCL)",
    @"Unspecified (non-VCL)",
    @"Unspecified (non-VCL)",
    @"Unspecified (non-VCL)",
    @"Unspecified (non-VCL)",
};


static GstFlowReturn new_sample(GstAppSink *sink, gpointer user_data)
{
    GStreamerBackend *backend = (__bridge GStreamerBackend *)(user_data);
    GstSample *sample = gst_app_sink_pull_sample(sink);
    GstBuffer *buffer = gst_sample_get_buffer(sample);
    GstMemory *memory = gst_buffer_get_all_memory(buffer);

    GstMapInfo info;
    gst_memory_map (memory, &info, GST_MAP_READ);

    int startCodeIndex = 0;
    for (int i = 0; i < 5; i++) {
        if (info.data[i] == 0x01) {
            startCodeIndex = i;
            break;
        }
    }
    int nalu_type = ((uint8_t)info.data[startCodeIndex + 1] & 0x1F);
    NSLog(@"NALU with Type \"%@\" received.", naluTypesStrings[nalu_type]);
    if(backend.searchForSPSAndPPS) {
        if (nalu_type == 7)
            backend.spsData = [NSData dataWithBytes:&(info.data[startCodeIndex + 1]) length: info.size - 4];

        if (nalu_type == 8)
            backend.ppsData = [NSData dataWithBytes:&(info.data[startCodeIndex + 1]) length: info.size - 4];

        if (backend.spsData != nil && backend.ppsData != nil) {
            const uint8_t* const parameterSetPointers[2] = { (const uint8_t*)[backend.spsData bytes], (const uint8_t*)[backend.ppsData bytes] };
            const size_t parameterSetSizes[2] = { [backend.spsData length], [backend.ppsData length] };

            CMVideoFormatDescriptionRef videoFormatDescr;
            OSStatus status = CMVideoFormatDescriptionCreateFromH264ParameterSets(kCFAllocatorDefault, 2, parameterSetPointers, parameterSetSizes, 4, &videoFormatDescr);
            [backend setVideoFormatDescr:videoFormatDescr];
            [backend setSearchForSPSAndPPS:false];
            NSLog(@"Found all data for CMVideoFormatDescription. Creation: %@.", (status == noErr) ? @"successfully." : @"failed.");
        }
    }
    if (nalu_type == 1 || nalu_type == 5) {
        CMBlockBufferRef videoBlock = NULL;
        OSStatus status = CMBlockBufferCreateWithMemoryBlock(NULL, info.data, info.size, kCFAllocatorNull, NULL, 0, info.size, 0, &videoBlock);
        NSLog(@"BlockBufferCreation: %@", (status == kCMBlockBufferNoErr) ? @"successfully." : @"failed.");
        const uint8_t sourceBytes[] = {(uint8_t)(info.size >> 24), (uint8_t)(info.size >> 16), (uint8_t)(info.size >> 8), (uint8_t)info.size};
        status = CMBlockBufferReplaceDataBytes(sourceBytes, videoBlock, 0, 4);
        NSLog(@"BlockBufferReplace: %@", (status == kCMBlockBufferNoErr) ? @"successfully." : @"failed.");

        CMSampleBufferRef sbRef = NULL;
        const size_t sampleSizeArray[] = {info.size};

        status = CMSampleBufferCreate(kCFAllocatorDefault, videoBlock, true, NULL, NULL, backend.videoFormatDescr, 1, 0, NULL, 1, sampleSizeArray, &sbRef);
        NSLog(@"SampleBufferCreate: %@", (status == noErr) ? @"successfully." : @"failed.");

        CFArrayRef attachments = CMSampleBufferGetSampleAttachmentsArray(sbRef, YES);
        CFMutableDictionaryRef dict = (CFMutableDictionaryRef)CFArrayGetValueAtIndex(attachments, 0);
        CFDictionarySetValue(dict, kCMSampleAttachmentKey_DisplayImmediately, kCFBooleanTrue);

        NSLog(@"Error: %@, Status:%@", backend.displayLayer.error, (backend.displayLayer.status == AVQueuedSampleBufferRenderingStatusUnknown)?@"unknown":((backend.displayLayer.status == AVQueuedSampleBufferRenderingStatusRendering)?@"rendering":@"failed"));
        dispatch_async(dispatch_get_main_queue(),^{
            [backend.displayLayer enqueueSampleBuffer:sbRef];
            [backend.displayLayer setNeedsDisplay];
        });

    }

    gst_memory_unmap(memory, &info);
    gst_memory_unref(memory);
    gst_buffer_unref(buffer);

    return GST_FLOW_OK;
}

@implementation GStreamerBackend

- (instancetype)init
{
    if (self = [super init]) {
        self.searchForSPSAndPPS = true;
        self.ppsData = nil;
        self.spsData = nil;
        self.displayLayer = [[AVSampleBufferDisplayLayer alloc] init];
        self.displayLayer.bounds = CGRectMake(0, 0, 300, 300);
        self.displayLayer.backgroundColor = [UIColor blackColor].CGColor;
        self.displayLayer.position = CGPointMake(500, 500);
        self.queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);
        dispatch_async(self.queue, ^{
            [self app_function];
        });
    }
    return self;
}

- (void)start
{
    if(gst_element_set_state(self.pipeline, GST_STATE_PLAYING) == GST_STATE_CHANGE_FAILURE) {
        NSLog(@"Failed to set pipeline to playing");
    }
}

- (void)app_function
{
    GstElement *udpsrc, *rtphdepay, *capsfilter;
    GMainContext *context; /* GLib context used to run the main loop */
    GMainLoop *main_loop;  /* GLib main loop */


    context = g_main_context_new ();
    g_main_context_push_thread_default(context);

    g_set_application_name ("appsink");

    self.pipeline = gst_pipeline_new ("testpipe");

    udpsrc = gst_element_factory_make ("udpsrc", "udpsrc");
    GstCaps *caps = gst_caps_new_simple("application/x-rtp", "media", G_TYPE_STRING, "video", "clock-rate", G_TYPE_INT, 90000, "encoding-name", G_TYPE_STRING, "H264", NULL);
    g_object_set(udpsrc, "caps", caps, "port", 5000, NULL);
    gst_caps_unref(caps);
    rtphdepay = gst_element_factory_make("rtph264depay", "rtph264depay");
    capsfilter = gst_element_factory_make("capsfilter", "capsfilter");
    caps = gst_caps_new_simple("video/x-h264", "streamformat", G_TYPE_STRING, "byte-stream", "alignment", G_TYPE_STRING, "nal", NULL);
    g_object_set(capsfilter, "caps", caps, NULL);
    self.appsink = gst_element_factory_make ("appsink", "appsink");

    gst_bin_add_many (GST_BIN (self.pipeline), udpsrc, rtphdepay, capsfilter, self.appsink, NULL);

    if(!gst_element_link_many (udpsrc, rtphdepay, capsfilter, self.appsink, NULL)) {
        NSLog(@"Cannot link gstreamer elements");
        exit (1);
    }

    if(gst_element_set_state(self.pipeline, GST_STATE_READY) != GST_STATE_CHANGE_SUCCESS)
        NSLog(@"could not change to ready");

    GstAppSinkCallbacks callbacks = { NULL, NULL, new_sample,
        NULL, NULL};
    gst_app_sink_set_callbacks (GST_APP_SINK(self.appsink), &callbacks, (__bridge gpointer)(self), NULL);

    main_loop = g_main_loop_new (context, FALSE);
    g_main_loop_run (main_loop);


    /* Free resources */
    g_main_loop_unref (main_loop);
    main_loop = NULL;
    g_main_context_pop_thread_default(context);
    g_main_context_unref (context);
    gst_element_set_state (GST_ELEMENT (self.pipeline), GST_STATE_NULL);
    gst_object_unref (GST_OBJECT (self.pipeline));
}

@end

What I get when running the App and starting to stream to the iOS device:

NALU with Type "Sequence parameter set (non-VCL)" received.
NALU with Type "Picture parameter set   (non-VCL)" received.

Found all data for CMVideoFormatDescription. Creation: successfully..

NALU with Type "Coded slice of an IDR picture (VCL)" received.
BlockBufferCreation: successfully.
BlockBufferReplace: successfully.
SampleBufferCreate: successfully.
Error: (null), Status:unknown

NALU with Type "Coded slice of a non-IDR picture (VCL)" received.
BlockBufferCreation: successfully.
BlockBufferReplace: successfully.
SampleBufferCreate: successfully.
Error: (null), Status:rendering
[...] (repetition of the last 5 lines)

So it seems to decode as it should do, but my problem is, that I could not see anything in my AVSampleBufferDisplayLayer. It might be a problem with the kCMSampleAttachmentKey_DisplayImmediately, but I have set it like I was told to here (see the 'important' note).

Every idea is welcome ;)

Answer 1

Got it working now. The length of each NALU does not contain the length header itself. So i have do subtract 4 from my info.size before using it for my sourceBytes.

Answer 2

Instructed by your code,I write an program to decode and display a live H.264 stream using AVSampleBufferDisplayLayer.I use live555 rather GSStream to receive H.264 NAL units.

Unfortunately, my app only displays a few frames and then no image can be show any more.Has you app ever met with the same problem?