How to cache a AVI file using ffMpeg - ffmpeg

Question

I am reading a AVI file using ffMpeg.
I want to cache the file into a vector and resuse it later.
This is my code.
typedef struct {
AVFormatContext *fmt_ctx;
int stream_idx;
AVStream *video_stream;
AVCodecContext *codec_ctx;
AVCodec *decoder;
AVPacket *packet;
AVFrame *av_frame;
AVFrame *gl_frame;
struct SwsContext *conv_ctx;
unsigned int frame_tex;
}AppData;
AppData data;
Here i am caching the file to a std::vector
std::vector< AVFrame* > cache;
bool initReadFrame()
{
do {
glBindTexture(GL_TEXTURE_2D, data.frame_tex);
int error = av_read_frame(data.fmt_ctx, data.packet);
if (error)
{
av_free_packet(data.packet);
return false;
}
if (data.packet->stream_index == data.stream_idx)
{
int frame_finished = 0;
if (avcodec_decode_video2(data.codec_ctx, data.av_frame, &frame_finished,
data.packet) < 0) {
av_free_packet(data.packet);
return false;
}
if (frame_finished)
{
if (!data.conv_ctx)
{
data.conv_ctx = sws_getContext(data.codec_ctx->width,
data.codec_ctx->height, data.codec_ctx->pix_fmt,
data.codec_ctx->width, data.codec_ctx->height, AV_PIX_FMT_RGBA,
SWS_BICUBIC, NULL, NULL, NULL);
}
sws_scale(data.conv_ctx, data.av_frame->data, data.av_frame->linesize, 0,
data.codec_ctx->height, data.gl_frame->data, data.gl_frame->linesize);
glTexSubImage2D(GL_TEXTURE_2D, 0, 0, 0, data.codec_ctx->width,
data.codec_ctx->height, GL_RGBA, GL_UNSIGNED_BYTE,
data.gl_frame->data[0]);
cache.push_back(av_frame_clone(data.gl_frame)); // Pushing AVFrame* to vector
}
}
av_free_packet(data.packet);
} while (data.packet->stream_index != data.stream_idx);
return true;
}
here i am trying to read the buffer and updating GL_TEXTURE_2D
void playCache()
{
glTexSubImage2D(GL_TEXTURE_2D, 0, 0, 0, data.codec_ctx->width,
data.codec_ctx->height, GL_RGBA, GL_UNSIGNED_BYTE,
cache[temp]->data[0]);
temp++;
}
The issue i am facing is that when i try to read the Cached data the application crashes.

Answer 1

You are storing dead reference in your cache.
cache.push_back(av_frame_clone(data.gl_frame));
the doc says:
av_frame_clone: Create a new frame that references the same data as src.
When you destroy src, you loose its content and you can't access it in your cache.
You can try to move the ref to your new frame, or to copies its value.
Move:
AVFrame* cachedValue;
av_frame_move_ref(cachedValue, data.gl_frame);
cache.push_back(cachedValue);
Copy
AVFrame *cachedValue= av_frame_alloc();
cachedValue->format = data.gl_frame->format;
cachedValue->width = data.gl_frame->width;
cachedValue->height = data.gl_frame->height;
cachedValue->channels = data.gl_frame->channels;
cachedValue->channel_layout = data.gl_frame->channel_layout;
cachedValue->nb_samples = data.gl_frame->nb_samples;
av_frame_get_buffer(cachedValue, 32);
av_frame_copy(cachedValue, data.gl_frame);
av_frame_copy_props(cachedValue, data.gl_frame);
cache.push_back(cachedValue);
/////////////////////////////////////////////////
avformat_network_init();
initializeAppData();
// open video
if (avformat_open_input(&data.fmt_ctx, stdstrPathOfVideo.c_str(), NULL, NULL) < 0) {
clearAppData();
return;
}
// find stream info
if (avformat_find_stream_info(data.fmt_ctx, NULL) < 0) {
clearAppData();
return;
}
// dump debug info
// av_dump_format(data.fmt_ctx, 0, "D:\\E\\Event\\2019\\AVI_Badges\\Generic\\Generic.avi", 0);
// find the video stream
for (unsigned int i = 0; i < data.fmt_ctx->nb_streams; ++i)
{
if (data.fmt_ctx->streams[i]->codec->codec_type == AVMEDIA_TYPE_VIDEO)
{
data.stream_idx = i;
break;
}
}
if (data.stream_idx == -1)
{
clearAppData();
return;
}
data.video_stream = data.fmt_ctx->streams[data.stream_idx];
data.codec_ctx = data.video_stream->codec;
// find the decoder
data.decoder = avcodec_find_decoder(data.codec_ctx->codec_id);
if (data.decoder == NULL)
{
clearAppData();
return;
}
// open the decoder
if (avcodec_open2(data.codec_ctx, data.decoder, NULL) < 0)
{
clearAppData();
return;
}
// allocate the video frames
data.av_frame = av_frame_alloc();
data.gl_frame = av_frame_alloc();
int size = avpicture_get_size(AV_PIX_FMT_RGBA, data.codec_ctx->width,
data.codec_ctx->height);
uint8_t *internal_buffer = (uint8_t *)av_malloc(size * sizeof(uint8_t));
avpicture_fill((AVPicture *)data.gl_frame, internal_buffer, AV_PIX_FMT_RGBA,
data.codec_ctx->width, data.codec_ctx->height);
data.packet = (AVPacket *)av_malloc(sizeof(AVPacket));