AVFrame to RGB - decoding artifacts - image

Question

I want to programmatically convert a mp4 video file (with h264 codec) to single RGB images. With the command line this looks like:
ffmpeg -i test1080.mp4 -r 30 image-%3d.jpg
Using this command produces a nice set of pictures. But when I try to programmatically do the same some images (probably B and P frames) look odd (e.g. have kind of distorted areas with difference information etc.). The reading and conversion code is as follow:
AVFrame *frame = avcodec_alloc_frame();
AVFrame *frameRGB = avcodec_alloc_frame();
AVPacket packet;
int buffer_size=avpicture_get_size(PIX_FMT_RGB24, m_codecCtx->width,
m_codecCtx->height);
uint8_t *buffer = new uint8_t[buffer_size];
avpicture_fill((AVPicture *)frameRGB, buffer, PIX_FMT_RGB24,
m_codecCtx->width, m_codecCtx->height);
while (true)
{
// Read one packet into `packet`
if (av_read_frame(m_formatCtx, &packet) < 0) {
break; // End of stream. Done decoding.
}
if (avcodec_decode_video(m_codecCtx, frame, &buffer_size, packet.data, packet.size) < 1) {
break; // Error in decoding
}
if (!buffer_size) {
break;
}
// Convert
img_convert((AVPicture *)frameRGB, PIX_FMT_RGB24, (AVPicture*)frame,
m_codecCtx->pix_fmt, m_codecCtx->width, m_codecCtx->height);
// RGB data is now available in frameRGB for further processing
}
How can I convert the video stream so that each final image shows all image data, so that information from B and P frames is included in all frames?
[EDIT:] A sample image showing the artifacts is here: http://imageshack.us/photo/my-images/201/sampleq.jpg/
Regards,

Answer 1

If the third argument of avcodec_decode_video returns a null value, it does not mean the error. This means that the frame is not yet ready. You need to continue to read frames until the value becomes nonzero.
if (!buffer_size) {
continue;
}
UPD
Try to add the check and display only the key frames, it will help isolate the problem.
while (true)
{
// Read one packet into `packet`
if (av_read_frame(m_formatCtx, &packet) < 0) {
break; // End of stream. Done decoding.
}
if (avcodec_decode_video(m_codecCtx, frame, &buffer_size,
packet.data, packet.size) < 1)
{
break; // Error in decoding
}
if (!buffer_size) {
continue; // <-- It's important!
}
// check for key frame
if (packet.flags & AV_PKT_FLAG_KEY)
{
// Convert
img_convert((AVPicture *)frameRGB, PIX_FMT_RGB24, (AVPicture*)frame,
m_codecCtx->pix_fmt, m_codecCtx->width, m_codecCtx->height);
}
}