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Rennes Emotion Map 2010-11
19 octobre 2011, par
Mis à jour : Juillet 2013
Langue : français
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FFmpeg.Autogen Wrapper : Issue with Zero-Sized Atom Boxes in MP4 Output
11 juin 2024, par Alexander JanssonI just started learning ffmpeg using ffmpeg.autogen wrapper version 5.1 in c#, and ffmpeg shared libs version 5.1. Im trying to facilitate a class which screenrecords using gdigrab and produces streamable mp4 to a/an buffer/event. Everything seems to work as suposed to with no error except that the outputstream produces atom boxes with 0 in size thus small file size aswell, no data seems to be produced in the boxes, the "debug test mp4 file" is analyzed with MP4Box and the box info is provided in the thread.


To be more specific why does this code produce empty atomboxes, is someone able to make the data produced actually contain any frame data from the gdigrab editing my code ?


`code :


public unsafe class ScreenStreamer : IDisposable
 {
 private readonly AVCodec* productionCodec;
 private readonly AVCodec* screenCaptureAVCodec;
 private readonly AVCodecContext* productionAVCodecContext;
 private readonly AVFormatContext* productionFormatContext;
 private readonly AVCodecContext* screenCaptureAVCodecContext;
 private readonly AVDictionary* productionAVCodecOptions;
 private readonly AVInputFormat* screenCaptureInputFormat;
 private readonly AVFormatContext* screenCaptureInputFormatContext;
 private readonly int gDIGrabVideoStreamIndex;
 private readonly System.Drawing.Size screenBounds;
 private readonly int _produceAtleastAmount;
 public EventHandler OnNewVideoDataProduced;
 private MemoryStream unsafeToManagedBridgeBuffer;
 private CancellationTokenSource cancellationTokenSource;
 private Task recorderTask;

 public ScreenStreamer(int fps, int bitrate, int screenIndex, int produceAtleastAmount = 1000)
 {
 ffmpeg.avdevice_register_all();
 ffmpeg.avformat_network_init();
 recorderTask = Task.CompletedTask;
 cancellationTokenSource = new CancellationTokenSource();
 unsafeToManagedBridgeBuffer = new MemoryStream();
 _produceAtleastAmount = produceAtleastAmount;

 // Allocate and initialize production codec and context
 productionCodec = ffmpeg.avcodec_find_encoder(AVCodecID.AV_CODEC_ID_H264);
 if (productionCodec == null) throw new ApplicationException("Could not find encoder for codec ID H264.");

 productionAVCodecContext = ffmpeg.avcodec_alloc_context3(productionCodec);
 if (productionAVCodecContext == null) throw new ApplicationException("Could not allocate video codec context.");

 // Set codec parameters
 screenBounds = RetrieveScreenBounds(screenIndex);
 productionAVCodecContext->width = screenBounds.Width;
 productionAVCodecContext->height = screenBounds.Height;
 productionAVCodecContext->time_base = new AVRational() { den = fps, num = 1 };
 productionAVCodecContext->pix_fmt = AVPixelFormat.AV_PIX_FMT_YUV420P;
 productionAVCodecContext->bit_rate = bitrate;

 int result = ffmpeg.av_opt_set(productionAVCodecContext->priv_data, "preset", "veryfast", 0);
 if (result != 0)
 {
 throw new ApplicationException($"Failed to set options with error code {result}.");
 }

 // Open codec
 fixed (AVDictionary** pm = &productionAVCodecOptions)
 {
 result = ffmpeg.av_dict_set(pm, "movflags", "frag_keyframe+empty_moov+default_base_moof", 0);
 if (result < 0)
 {
 throw new ApplicationException($"Failed to set dictionary with error code {result}.");
 }

 result = ffmpeg.avcodec_open2(productionAVCodecContext, productionCodec, pm);
 if (result < 0)
 {
 throw new ApplicationException($"Failed to open codec with error code {result}.");
 }
 }

 // Allocate and initialize screen capture codec and context
 screenCaptureInputFormat = ffmpeg.av_find_input_format("gdigrab");
 if (screenCaptureInputFormat == null) throw new ApplicationException("Could not find input format gdigrab.");

 fixed (AVFormatContext** ps = &screenCaptureInputFormatContext)
 {
 result = ffmpeg.avformat_open_input(ps, "desktop", screenCaptureInputFormat, null);
 if (result < 0)
 {
 throw new ApplicationException($"Failed to open input with error code {result}.");
 }

 result = ffmpeg.avformat_find_stream_info(screenCaptureInputFormatContext, null);
 if (result < 0)
 {
 throw new ApplicationException($"Failed to find stream info with error code {result}.");
 }
 }

 gDIGrabVideoStreamIndex = -1;
 for (int i = 0; i < screenCaptureInputFormatContext->nb_streams; i++)
 {
 if (screenCaptureInputFormatContext->streams[i]->codecpar->codec_type == AVMediaType.AVMEDIA_TYPE_VIDEO)
 {
 gDIGrabVideoStreamIndex = i;
 break;
 }
 }

 if (gDIGrabVideoStreamIndex < 0)
 {
 throw new ApplicationException("Failed to find video stream in input.");
 }

 AVCodecParameters* codecParameters = screenCaptureInputFormatContext->streams[gDIGrabVideoStreamIndex]->codecpar;
 screenCaptureAVCodec = ffmpeg.avcodec_find_decoder(codecParameters->codec_id);
 if (screenCaptureAVCodec == null)
 {
 throw new ApplicationException("Could not find decoder for screen capture.");
 }

 screenCaptureAVCodecContext = ffmpeg.avcodec_alloc_context3(screenCaptureAVCodec);
 if (screenCaptureAVCodecContext == null)
 {
 throw new ApplicationException("Could not allocate screen capture codec context.");
 }

 result = ffmpeg.avcodec_parameters_to_context(screenCaptureAVCodecContext, codecParameters);
 if (result < 0)
 {
 throw new ApplicationException($"Failed to copy codec parameters to context with error code {result}.");
 }

 result = ffmpeg.avcodec_open2(screenCaptureAVCodecContext, screenCaptureAVCodec, null);
 if (result < 0)
 {
 throw new ApplicationException($"Failed to open screen capture codec with error code {result}.");
 }
 }

 public void Start()
 {
 recorderTask = Task.Run(() =>
 {
 AVPacket* packet = ffmpeg.av_packet_alloc();
 AVFrame* rawFrame = ffmpeg.av_frame_alloc();
 AVFrame* compatibleFrame = null;
 byte* dstBuffer = null;

 try
 {
 while (!cancellationTokenSource.Token.IsCancellationRequested)
 {
 if (ffmpeg.av_read_frame(screenCaptureInputFormatContext, packet) >= 0)
 {
 if (packet->stream_index == gDIGrabVideoStreamIndex)
 {
 int response = ffmpeg.avcodec_send_packet(screenCaptureAVCodecContext, packet);
 if (response < 0)
 {
 throw new ApplicationException($"Error while sending a packet to the decoder: {response}");
 }

 response = ffmpeg.avcodec_receive_frame(screenCaptureAVCodecContext, rawFrame);
 if (response == ffmpeg.AVERROR(ffmpeg.EAGAIN) || response == ffmpeg.AVERROR_EOF)
 {
 continue;
 }
 else if (response < 0)
 {
 throw new ApplicationException($"Error while receiving a frame from the decoder: {response}");
 }

 compatibleFrame = ConvertToCompatiblePixelFormat(rawFrame, out dstBuffer);

 response = ffmpeg.avcodec_send_frame(productionAVCodecContext, compatibleFrame);
 if (response < 0)
 {
 throw new ApplicationException($"Error while sending a frame to the encoder: {response}");
 }

 while (response >= 0)
 {
 response = ffmpeg.avcodec_receive_packet(productionAVCodecContext, packet);
 if (response == ffmpeg.AVERROR(ffmpeg.EAGAIN) || response == ffmpeg.AVERROR_EOF)
 {
 break;
 }
 else if (response < 0)
 {
 throw new ApplicationException($"Error while receiving a packet from the encoder: {response}");
 }

 using var packetStream = new UnmanagedMemoryStream(packet->data, packet->size);
 packetStream.CopyTo(unsafeToManagedBridgeBuffer);
 byte[] managedBytes = unsafeToManagedBridgeBuffer.ToArray();
 OnNewVideoDataProduced?.Invoke(this, managedBytes);
 unsafeToManagedBridgeBuffer.SetLength(0);
 }
 }
 }
 ffmpeg.av_packet_unref(packet);
 ffmpeg.av_frame_unref(rawFrame);
 if (compatibleFrame != null)
 {
 ffmpeg.av_frame_unref(compatibleFrame);
 ffmpeg.av_free(dstBuffer);
 }
 }
 }
 finally
 {
 ffmpeg.av_packet_free(&packet);
 ffmpeg.av_frame_free(&rawFrame);
 if (compatibleFrame != null)
 {
 ffmpeg.av_frame_free(&compatibleFrame);
 }
 }
 });
 }

 public AVFrame* ConvertToCompatiblePixelFormat(AVFrame* srcFrame, out byte* dstBuffer)
 {
 AVFrame* dstFrame = ffmpeg.av_frame_alloc();
 int buffer_size = ffmpeg.av_image_get_buffer_size(productionAVCodecContext->pix_fmt, productionAVCodecContext->width, productionAVCodecContext->height, 1);
 byte_ptrArray4 dstData = new byte_ptrArray4();
 int_array4 dstLinesize = new int_array4();
 dstBuffer = (byte*)ffmpeg.av_malloc((ulong)buffer_size);
 ffmpeg.av_image_fill_arrays(ref dstData, ref dstLinesize, dstBuffer, productionAVCodecContext->pix_fmt, productionAVCodecContext->width, productionAVCodecContext->height, 1);

 dstFrame->format = (int)productionAVCodecContext->pix_fmt;
 dstFrame->width = productionAVCodecContext->width;
 dstFrame->height = productionAVCodecContext->height;
 dstFrame->data.UpdateFrom(dstData);
 dstFrame->linesize.UpdateFrom(dstLinesize);

 SwsContext* swsCtx = ffmpeg.sws_getContext(
 srcFrame->width, srcFrame->height, (AVPixelFormat)srcFrame->format,
 productionAVCodecContext->width, productionAVCodecContext->height, productionAVCodecContext->pix_fmt,
 ffmpeg.SWS_BILINEAR, null, null, null);

 if (swsCtx == null)
 {
 throw new ApplicationException("Could not initialize the conversion context.");
 }

 ffmpeg.sws_scale(swsCtx, srcFrame->data, srcFrame->linesize, 0, srcFrame->height, dstFrame->data, dstFrame->linesize);
 ffmpeg.sws_freeContext(swsCtx);
 return dstFrame;
 }

 private System.Drawing.Size RetrieveScreenBounds(int screenIndex)
 {
 return new System.Drawing.Size(1920, 1080);
 }

 public void Dispose()
 {
 cancellationTokenSource?.Cancel();
 recorderTask?.Wait();
 cancellationTokenSource?.Dispose();
 recorderTask?.Dispose();
 unsafeToManagedBridgeBuffer?.Dispose();

 fixed (AVCodecContext** p = &productionAVCodecContext)
 {
 if (*p != null)
 {
 ffmpeg.avcodec_free_context(p);
 }
 }
 fixed (AVCodecContext** p = &screenCaptureAVCodecContext)
 {
 if (*p != null)
 {
 ffmpeg.avcodec_free_context(p);
 }
 }

 if (productionFormatContext != null)
 {
 ffmpeg.avformat_free_context(productionFormatContext);
 }

 if (screenCaptureInputFormatContext != null)
 {
 ffmpeg.avformat_free_context(screenCaptureInputFormatContext);
 }

 if (productionAVCodecOptions != null)
 {
 fixed (AVDictionary** p = &productionAVCodecOptions)
 {
 ffmpeg.av_dict_free(p);
 }
 }
 }
 }


I call Start method and wait 8 econds, out of scope I write the bytes to an mp4 file without using the write trailer just to debug the atomboxes. and the mp4 debugging box output I got :


(Full OUTPUT)
https://pastebin.com/xkM4MfG7



(Not full)




"
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"
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-
FFMPEG lossless simple & efficient format
30 octobre 2016, par AdminyI took a sample video and ran this code for each image format like this :
ffmpeg -i test.mkv png/%d.png
ffmpeg -i test.mkv bmp/%d.bmpWhat I noted is that BMP at 1080P has a fixed size of 5.97 MB (6,266,934 bytes)
!6,220,800Then I did some maths :
1 byte = 2^8 == 256 possible combinations
r + g + b form a color (0-255,0-255,0-255)
bmp = 3 * 1920 * 1080 = 6,220,800 bytesSo extra is just the file headers ?! (46134 bytes for just headers ?)
Next thing I noted that PNG size is dynamic and when the image has a lot of repetition is somewhere 2.5mb. Usually its between 10mb and 12mb.
Also decoding BMP seemed a lot quicker compared to PNG. So there is no point in even looking at PNG. I would like to know why is it so huge over BMP if it has (zlib) compression factor.
What is the best format to export to in terms of speed and size, preferred if its as simple as reading the file of color bytes ?
-
How to extract frames at 30 fps using FFMPEG APIs ?
7 septembre 2016, par Amber BeriwalWe are working on a project that consumes
FFMPEGlibrary for video frame extraction.We have seen that using command line, ffmpeg is capable of extracting frames at 30 fps using below command. Even using Xuggler, we are able to extract frames at 30 fps.
ffmpeg -i input.flv -vf fps=1 out%d.pngBut when we use FFMPEG APIs directly in our code, we are getting following results :
- 720p video (1280 x 720) - 16 fps (approx. 60 ms/frame)
- 1080p video (1920 x 1080) - 7 fps (approx. 140 ms/frame)
Ideally, we should be able to get the data in constant time (approx. 30 ms/frame).
How can we get 30 fps ?
Code :
if (avformat_open_input(&pFormatCtx, pcVideoFile, NULL, NULL)) {
iError = -1; //Couldn't open file
}
if (!iError) {
//Retrieve stream information
if (avformat_find_stream_info(pFormatCtx, NULL) < 0)
iError = -2; //Couldn't find stream information
}
//Find the first video stream
if (!iError) {
for (i = 0; i < pFormatCtx->nb_streams; i++) {
if (AVMEDIA_TYPE_VIDEO
== pFormatCtx->streams[i]->codec->codec_type) {
iFramesInVideo = pFormatCtx->streams[i]->nb_index_entries;
duration = pFormatCtx->streams[i]->duration;
begin = pFormatCtx->streams[i]->start_time;
time_base = (pFormatCtx->streams[i]->time_base.num * 1.0f)
/ pFormatCtx->streams[i]->time_base.den;
pCodecCtx = avcodec_alloc_context3(NULL);
if (!pCodecCtx) {
iError = -6;
break;
}
AVCodecParameters params = { 0 };
iReturn = avcodec_parameters_from_context(&params,
pFormatCtx->streams[i]->codec);
if (iReturn < 0) {
iError = -7;
break;
}
iReturn = avcodec_parameters_to_context(pCodecCtx, &params);
if (iReturn < 0) {
iError = -7;
break;
}
//pCodecCtx = pFormatCtx->streams[i]->codec;
iVideoStreamIndex = i;
break;
}
}
}
if (!iError) {
if (iVideoStreamIndex == -1) {
iError = -3; // Didn't find a video stream
}
}
if (!iError) {
// Find the decoder for the video stream
pCodec = avcodec_find_decoder(pCodecCtx->codec_id);
if (pCodec == NULL) {
iError = -4;
}
}
if (!iError) {
// Open codec
if (avcodec_open2(pCodecCtx, pCodec, NULL) < 0)
iError = -5;
}
if (!iError) {
iNumBytes = av_image_get_buffer_size(AV_PIX_FMT_RGB24, pCodecCtx->width,
pCodecCtx->height, 1);
// initialize SWS context for software scaling
sws_ctx = sws_getContext(pCodecCtx->width, pCodecCtx->height,
pCodecCtx->pix_fmt, pCodecCtx->width, pCodecCtx->height,
AV_PIX_FMT_RGB24,
SWS_BILINEAR,
NULL,
NULL,
NULL);
if (!sws_ctx) {
iError = -7;
}
}
clock_gettime(CLOCK_MONOTONIC_RAW, &end);
delta_us = (end.tv_sec - start.tv_sec) * 1000000
+ (end.tv_nsec - start.tv_nsec) / 1000;
start = end;
//LOGI("Starting_Frame_Extraction: %lld", delta_us);
if (!iError) {
while (av_read_frame(pFormatCtx, &packet) == 0) {
// Is this a packet from the video stream?
if (packet.stream_index == iVideoStreamIndex) {
pFrame = av_frame_alloc();
if (NULL == pFrame) {
iError = -8;
break;
}
// Decode video frame
avcodec_decode_video2(pCodecCtx, pFrame, &iFrameFinished,
&packet);
if (iFrameFinished) {
//OUR CODE
}
av_frame_free(&pFrame);
pFrame = NULL;
}
av_packet_unref(&packet);
}
}
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