FFmpeg api iOS "Resource temporarily unavailable" - ios

Question

I've spent hours trying to fix this:
I'm trying to use the ffmpeg api on iOS. My Xcode project is building and I can call ffmpeg api functions. I am trying to write code that decodes a video (Without outputting anything for now), and I keep getting error -35: "Resource temporarily unavailable".
The input file is from the camera roll (.mov) and I'm using Mpeg-4 for decoding. All I'm currently doing is getting data from the file, parsing it and sending the parsed packets to the decoder. When I try to get frames, all I get is an error. Does anyone know what I'm doing wrong?
+(void)test: (NSString*)filename outfile:(NSString*)outfilename {
/* register all the codecs */
avcodec_register_all();
AVCodec *codec;
AVCodecParserContext *parser;
AVCodecContext *c= NULL;
int frame_count;
FILE* f;
AVFrame* frame;
AVPacket* avpkt;
avpkt = av_packet_alloc();
//av_init_packet(avpkt);
char buf[1024];
uint8_t inbuf[INBUF_SIZE + AV_INPUT_BUFFER_PADDING_SIZE];
uint8_t *data;
size_t data_size;
/* set end of buffer to 0 (this ensures that no overreading happens for damaged mpeg streams) */
memset(inbuf + INBUF_SIZE, 0, AV_INPUT_BUFFER_PADDING_SIZE);
printf("Decode video file %s to %s\n", [filename cStringUsingEncoding:NSUTF8StringEncoding], [outfilename cStringUsingEncoding:NSUTF8StringEncoding]);
/* find the h264 video decoder */
codec = avcodec_find_decoder(AV_CODEC_ID_MPEG4);
if (!codec) {
fprintf(stderr, "Codec not found\n");
exit(1);
}
c = avcodec_alloc_context3(codec);
if (!c) {
fprintf(stderr, "Could not allocate video codec context\n");
exit(1);
}
if (codec->capabilities & AV_CODEC_CAP_TRUNCATED)
c->flags |= AV_CODEC_FLAG_TRUNCATED; // we do not send complete frames
/* For some codecs, such as msmpeg4 and mpeg4, width and height
MUST be initialized there because this information is not
available in the bitstream. */
/* open it */
if (avcodec_open2(c, codec, NULL) < 0) {
fprintf(stderr, "Could not open codec\n");
exit(1);
}
f = fopen([filename cStringUsingEncoding:NSUTF8StringEncoding], "rb");
if (!f) {
fprintf(stderr, "Could not open %s\n", [filename cStringUsingEncoding:NSUTF8StringEncoding]);
exit(1);
}
frame = av_frame_alloc();
if (!frame) {
fprintf(stderr, "Could not allocate video frame\n");
exit(1);
}
frame_count = 0;
parser = av_parser_init(codec->id);
if (!parser) {
fprintf(stderr, "parser not found\n");
exit(1);
}
while (!feof(f)) {
/* read raw data from the input file */
data_size = fread(inbuf, 1, INBUF_SIZE, f);
if (!data_size)
break;
/* use the parser to split the data into frames */
data = inbuf;
while (data_size > 0) {
int ret = av_parser_parse2(parser, c, &avpkt->data, &avpkt->size, data, data_size, AV_NOPTS_VALUE, AV_NOPTS_VALUE, 0);
if (ret < 0) {
fprintf(stderr, "Error while parsing\n");
exit(1);
}
data += ret;
data_size -= ret;
if (avpkt->size){
char buf[1024];
ret = avcodec_send_packet(c, avpkt);
if (ret < 0) {
fprintf(stderr, "Error sending a packet for decoding\n");
continue;
exit(1);
}
while (ret >= 0) {
ret = avcodec_receive_frame(c, frame);
if (ret == AVERROR(EAGAIN) || ret == AVERROR_EOF){
char e [1024];
av_strerror(ret, e, 1024);
fprintf(stderr, "Fail: %s !\n", e);
// ~~~~~~~~ This is where my program exits ~~~~~~~~~~~~~~~~~~~~~~~~~~~
return;
}
else if (ret < 0) {
fprintf(stderr, "Error during decoding\n");
exit(1);
}
}
}
}
}
/* some codecs, such as MPEG, transmit the I and P frame with a
latency of one frame. You must do the following to have a
chance to get the last frame of the video */
fclose(f);
avcodec_close(c);
av_free(c);
av_frame_free(&frame);
printf("\n");
}

Answer 1

AVERROR(EAGAIN) is not an error, it just means output is not yet available and you need to call _send_packet() a few more times before the first output will be available from _receive_frame().
The output is buffered (delayed) to allow for B-frames and frame threading.