Video quality lost when converting from .ogg to .mp4

[William Metcalf]

Hello all,

I have written a gstreamer C application to convert a .ogg to .mp4 
file.  The application is successful at converting the video and audio, 
but the video produced after the conversion is of much lower quality 
than the original video ( the audio converts with basically no loss I 
can see).  I figure that some loss in video is to be expected, but I was 
wondering what gstreamer modules might be good for helping lower the 
loss in video quality.  Below is a snippet of my code that shows the 
pipeline I used to convert the file.

Thank you in advance for your help.

int main (int argc, char *argv[])
{
     gst_init(&argc, &argv);

     AV = 0;

     loop = g_main_loop_new(NULL, FALSE);

     /* Create elements */
     pipeline            = gst_pipeline_new("audio-player");

     /* Element for reading in a file */
     source                = gst_element_factory_make("filesrc", 
"file-source");

     /* OGG elements */
     oggdemuxer            = gst_element_factory_make("oggdemux", 
"ogg-demuxer");
     vorbis_decoder        = gst_element_factory_make("vorbisdec", 
"vorbis-decoder");
     theora_decoder        = gst_element_factory_make("theoradec", 
"theora-decoder");

     /* MP4 elements */
     audio_encoder        = gst_element_factory_make("faac", "aac-encoder");
     video_encoder        = gst_element_factory_make("ffenc_mpeg4", 
"avc-encoder");
     mp4_muxer            = gst_element_factory_make("qtmux", "mp4-muxer");

     /* Audio/Video elements */
     video_converter        = 
gst_element_factory_make("ffmpegcolorspace", "video-converter");
     videosink            = gst_element_factory_make("autovideosink", 
"video-sink");
     video_scale            = gst_element_factory_make("videoscale", 
"video-scale");
     video_rate            = gst_element_factory_make("videorate", 
"video-rate");
     audio_resample        = gst_element_factory_make("audioresample", 
"audio-resample");
     audio_rate            = gst_element_factory_make("audiorate", 
"audio-rate");
     audiosink            = gst_element_factory_make("autoaudiosink", 
"audio-sink");
     audio_converter        = gst_element_factory_make("audioconvert", 
"audio-converter");

     /* Queues */
     video_queue            = gst_element_factory_make("queue", 
"video-queue");
     audio_queue            = gst_element_factory_make("queue", 
"audio-queue");
     video_out_queue        = gst_element_factory_make("queue", 
"video-out-queue");
     audio_out_queue        = gst_element_factory_make("queue", 
"audio-out-queue");

     /* Element to write to the file */
     filesink                = gst_element_factory_make("filesink", 
"file-sink");

     /* Make sure we were able to create all of the elements*/
     if(!pipeline || !source || !oggdemuxer || !vorbis_decoder || 
!theora_decoder || !audio_encoder || !video_encoder || !mp4_muxer || 
!audio_converter || !video_converter || !audio_resample || !audio_rate 
|| !videosink || !audiosink || !video_queue || !audio_queue || 
!video_out_queue || !audio_out_queue || !video_scale || !video_rate || 
!filesink )
     {
         g_printerr("One ore more elements could not be created. 
Exiting.\n");
         return -1;
     }

     /* Input file */
     g_object_set(G_OBJECT(source), "location", "c:\\video(1080p).ogg", 
NULL);
     g_object_set(G_OBJECT(filesink), "location", 
"c:\\Encoder_Output\\video(encoded from ogg).mp4", NULL);

     /* Add a message handler from pipeline bus */
     bus = gst_pipeline_get_bus(GST_PIPELINE(pipeline));
     gst_bus_add_watch(bus, bus_call, loop);
     gst_object_unref(bus);

     /* add elements to the pipeline */
     gst_bin_add_many(GST_BIN(pipeline), source, oggdemuxer, 
video_queue, theora_decoder, video_converter, video_scale, video_rate, 
video_encoder, video_out_queue, audio_queue, vorbis_decoder, 
audio_converter, audio_resample, audio_rate, audio_encoder, 
audio_out_queue, mp4_muxer, filesink, NULL);

     /* link the elements together */
     res = gst_element_link(source, oggdemuxer);
     if(!res)
     {
         g_printerr("There was a problem linking filesrc to oggdemux.\n");
         return 1;
     }

     /* video_queue -> theoradec -> ffmpegcolorspace -> ffenc_mpeg4 -> 
video_out_queue ~> qtmux */
     res = gst_element_link_many(video_queue, theora_decoder, 
video_converter, video_scale, video_rate, video_encoder, 
video_out_queue, NULL);
     if(!res)
     {
         g_printerr("There was a problem linking video elements.\n");
         return 1;
     }
     //link_video_caps(video_scale, video_encoder, 854, 480, 25, 1);

     /* queue_audio -> vorbisdec -> audioconvert -> faac -> 
audio_out_queue ~> qtmux */
     res = gst_element_link_many(audio_queue, vorbis_decoder, 
audio_converter, audio_resample, audio_rate, audio_encoder, 
audio_out_queue, NULL);
     if(!res)
     {
         g_printerr("There was a problem linking the audio elements.\n");
         return 1;
     }
     g_signal_connect(oggdemuxer, "pad-added", G_CALLBACK(on_pad_added), 
NULL);

     /* qtmux -> filesink */
     res = gst_element_link(mp4_muxer, filesink);
     if(!res)
     {
         g_printerr("There was a problem linking qtmux to filesink.\n");
         return 1;
     }

     link_video_to_multiplexer(video_out_queue, mp4_muxer);
     link_audio_to_multiplexer(audio_out_queue, mp4_muxer);


     /* Set the pipeline stat to play and start the main loop*/
     g_print("Starting the pipeline\n");
     gst_element_set_state(pipeline, GST_STATE_PLAYING);
     g_main_loop_run(loop);

     /* We are done now, do a little bit of cleaning up */
     g_print("Stopping the pipeline.\n");
     gst_element_set_state(pipeline, GST_STATE_NULL);
     gst_object_unref(GST_OBJECT(pipeline));

     return 0;
}