基于案例1,我开始开发一个应用程序,应该可以从GStreamer获取一个H264-RTP-UDP-Stream,将其下载到一个“appsink”元素中,以直接访问NAL单元并执行转换创建CMSampleBuffers,我的AVSampleBufferDisplayLayer可以显示.

有趣的代码如下：

//
//  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)",@"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)",@"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,&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,4);
        NSLog(@"BlockBufferReplace: %@",(status == kCMBlockBufferNoErr) ? @"successfully." : @"Failed.");

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

        status = CMSampleBufferCreate(kcfAllocatorDefault,true,backend.videoFormatDescr,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(0,300,300);
        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","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","byte-stream","alignment","nal",NULL);
    g_object_set(capsfilter,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,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,new_sample,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

运行应用程序并开始流式传输到iOS设备时所获得的内容：

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)

所以似乎解码,因为它应该做,但我的问题是,我看不到任何东西在我的AVSampleBufferDisplayLayer.
这可能是kCMSampleAttachmentKey_DisplayImmediately的一个问题,但我已经设置好像我被告知到here (see the ‘important’ note).

欢迎每一个想法;)