Hi,
I'm just getting started using the ffmpeg libraries and am seeing a
problem when demuxing/decoding an FLV file. I'm attaching the sample
program which is basically just Martin Böhme's overview. My code was
originally somewhat more complicated so I've reverted to the attached
code. I understand that the code is not clean but it serves to show
what I'm seeing. If I run the code against an .flv file on the local
file system, the code runs fine to completion. If I access the same
file placed on a web server, I receive a series of "skipping flv packet"
errors toward the end of the decode. These seem to continue on
indefinitely. Here are the two outputs, from a good run (with a local
file) and an problem run pulling the file from a web server (The file is
still available on the server if anyone is interested).
c:> using_libavcoded.exe c:\temp\test.flv
reading c:\temp\test.flv
Input #0, flv, from 'c:\temp\test.flv':
Duration: 00:01:30.13, start: 0.000000, bitrate: 48 kb/s
Stream #0.0: Video: flv, yuv420p, 320x240, 15.00 tb(r)
Stream #0.1: Audio: mp3, 44100 Hz, mono, 48 kb/s
[flv @ 00B43670]warning: first frame is no keyframe
...........................................................................................
...........................................................................................
...........................................................................................
...................................................done
C:>using_libavcoded.exe http://www.oberholtzer.net/test.flv
reading http://www.oberholtzer.net/test.flv
Input #0, flv, from 'http://www.oberholtzer.net/test.flv':
Duration: 00:01:30.13, start: 0.000000, bitrate: 48 kb/s
Stream #0.0: Video: flv, yuv420p, 320x240, 15.00 tb(r)
Stream #0.1: Audio: mp3, 44100 Hz, mono, 48 kb/s
[flv @ 00B43670]warning: first frame is no keyframe
...............................................................................................
...............................................................................................
...............................................................................................
...................................................[flv @
00B29C6C]skipping flv packet: type 68, size 6386789, flags 0
[flv @ 00B29C6C]skipping flv packet: type 68, size 6386789, flags 0
[flv @ 00B29C6C]skipping flv packet: type 68, size 6386789, flags 0
[flv @ 00B29C6C]skipping flv packet: type 68, size 6386789, flags 0
[flv @ 00B29C6C]skipping flv packet: type 68, size 6386789, flags 0
These messages continue on. Am I doing something wrong that is causing
these messages?
Thanks for you help,
Brian
// using_libavcoded.cpp : Defines the entry point for the console application.
//
#include "stdafx.h"
extern "C"
{
#include "libavformat\avformat.h"
}
bool GetNextFrame(AVFormatContext *pFormatCtx, AVCodecContext *pCodecCtx,
int videoStream, AVFrame *pFrame)
{
static AVPacket packet;
static int bytesRemaining=0;
static uint8_t *rawData;
static bool fFirstTime=true;
int bytesDecoded;
int frameFinished;
// First time we're called, set packet.data to NULL to indicate it
// doesn't have to be freed
if(fFirstTime)
{
fFirstTime=false;
packet.data=NULL;
}
// Decode packets until we have decoded a complete frame
while(true)
{
// Work on the current packet until we have decoded all of it
while(bytesRemaining > 0)
{
// Decode the next chunk of data
bytesDecoded=avcodec_decode_video(pCodecCtx, pFrame,
&frameFinished, rawData, bytesRemaining);
// Was there an error?
if(bytesDecoded < 0)
{
fprintf(stderr, "Error while decoding frame\n");
return false;
}
bytesRemaining-=bytesDecoded;
rawData+=bytesDecoded;
// Did we finish the current frame? Then we can return
if(frameFinished)
return true;
}
// Read the next packet, skipping all packets that aren't for this
// stream
do
{
// Free old packet
if(packet.data!=NULL)
av_free_packet(&packet);
// Read new packet
if(av_read_packet(pFormatCtx, &packet)<0)
goto loop_exit;
} while(packet.stream_index!=videoStream);
bytesRemaining=packet.size;
rawData=packet.data;
}
loop_exit:
// Decode the rest of the last frame
bytesDecoded=avcodec_decode_video(pCodecCtx, pFrame, &frameFinished,
rawData, bytesRemaining);
// Free last packet
if(packet.data!=NULL)
av_free_packet(&packet);
return frameFinished!=0;
}
int _tmain(int argc, char* argv[])
{
av_register_all();
AVFormatContext *pFormatCtx;
const char *filename=argv[1];
printf("reading %s\n", filename );
// Open video file
if(av_open_input_file(&pFormatCtx, filename, NULL, 0, NULL)!=0)
return -1; // Couldn't open file
// Retrieve stream information
if(av_find_stream_info(pFormatCtx)<0)
-1; // Couldn't find stream information
dump_format(pFormatCtx, 0, filename, false);
unsigned int i, videoStream;
AVCodecContext *pCodecCtx;
// Find the first video stream
videoStream=-1;
for(i=0; i<pFormatCtx->nb_streams; i++)
if(pFormatCtx->streams[i]->codec->codec_type ==
CODEC_TYPE_VIDEO)
{
videoStream=i;
break;
}
if(videoStream==-1)
return -1; // Didn't find a video stream
// Get a pointer to the codec context for the video stream
pCodecCtx= pFormatCtx->streams[videoStream]->codec;
AVCodec *pCodec;
// Find the decoder for the video stream
pCodec=avcodec_find_decoder(pCodecCtx->codec_id);
if(pCodec==NULL)
return -1; // Codec not found
// Inform the codec that we can handle truncated bitstreams -- i.e.,
// bitstreams where frame boundaries can fall in the middle of packets
if(pCodec->capabilities & CODEC_CAP_TRUNCATED)
pCodecCtx->flags|=CODEC_FLAG_TRUNCATED;
// Open codec
if(avcodec_open(pCodecCtx, pCodec)<0)
return -1; // Could not open codec
AVFrame *pFrame;
pFrame=avcodec_alloc_frame();
while(GetNextFrame(pFormatCtx, pCodecCtx, videoStream, pFrame))
{
printf(".");
// doing nothing with the image
}
printf("done\n");
}
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