To be clearer, I modified the decoding_encoding.c example in ffmpeg to cause
the problem.
I basically changed the video_encode_example() to encode 1 second worth of
video and then flush the delayed frame. The code below is exactly the same
except 25 frames was replaced with 1 frame.
Now if I take this code block and duplicate it again, so that it basically runs
twice, the second avcodec_encode_video2() will hang.
/* encode 1 second of video */
for(i=0;i<1;i++) {
av_init_packet(&pkt);
pkt.data = NULL; // packet data will be allocated by the encoder
pkt.size = 0;
fflush(stdout);
/* prepare a dummy image */
/* Y */
for(y=0;y<c->height;y++) {
for(x=0;x<c->width;x++) {
frame->data[0][y * frame->linesize[0] + x] = x + y + i * 3;
}
}
/* Cb and Cr */
for(y=0;y<c->height/2;y++) {
for(x=0;x<c->width/2;x++) {
frame->data[1][y * frame->linesize[1] + x] = 128 + y + i * 2;
frame->data[2][y * frame->linesize[2] + x] = 64 + x + i * 5;
}
}
frame->pts = i;
/* encode the image */
ret = avcodec_encode_video2(c, &pkt, frame, &got_output);
if (ret < 0) {
fprintf(stderr, "Error encoding frame\n");
exit(1);
}
if (got_output) {
printf("Write frame %3d (size=%5d)\n", i, pkt.size);
fwrite(pkt.data, 1, pkt.size, f);
av_free_packet(&pkt);
}
}
/* get the delayed frames */
for (got_output = 1; got_output; i++) {
fflush(stdout);
ret = avcodec_encode_video2(c, &pkt, NULL, &got_output);
if (ret < 0) {
fprintf(stderr, "Error encoding frame\n");
exit(1);
}
if (got_output) {
printf("Write frame %3d (size=%5d)\n", i, pkt.size);
fwrite(pkt.data, 1, pkt.size, f);
av_free_packet(&pkt);
}
}
From: [email protected] [mailto:[email protected]] On
Behalf Of Ashwin Chandra - SISA
Sent: Thursday, February 07, 2013 3:08 PM
To: [email protected]
Subject: [Libav-user] Problem with using libavcodec with AV_CODEC_ID_H264
I have some code that takes a running stream of uncompressed video data and
encodes it using AV_CODEC_ID_H264.
The sequence I follow is
1. Call avcodec_encode_video2 on the AVFrame which contains my uncompressed
frame.
2. Call avcodec_encode_video2 again passing NULL in the AVFrame parameter.
3. Repeat 2. Until a frame arrives from the encoder.
This seems to work fine if the codec is MPEG2, but with H264, it hangs inside
avcodec_encode_video2 at step 2) on the second frame. I don't have debug
symbols and can't figure out why. Does there need to be a minimum set of
uncompressed data in the encoder before trying to flush out an encoded frame
for H264? If so, how do I know when it is safe to flush a frame?
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